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Astronomers Uncover Mystery Of The Magnetic World Of Galaxies

September 6, 2017 by  
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Astronomers have detected the magnetic field of a galaxy located a whopping 5 billion light-years from Earth. 

“This finding is exciting,” Sui Ann Mao, an astronomer from the Max Planck Institute for Radio Astronomy in Germany, said in a statement. “It is now the record holder of the most distant galaxy for which we have this magnetic-field information.”

Mao led the team that made the find. The researchers used the Karl G. Jansky Very Large Array, a radio telescope network in New Mexico, to detect and characterize the magnetic field of the distant galaxy.

“This means that magnetism is generated very early in a galaxy’s life by natural processes, and thus that almost every heavenly body is magnetic,” study co-author Bryan Gaensler, a professor at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto, said in the same statement. “The implication is that we need to understand magnetism to understand the universe.”

Measuring the magnetic fields of other galaxies that are at different distances from Earth and are different ages can help astronomers better understand how cosmic magnetism evolves, study team members said. Since a faraway magnetic field can’t be detected directly, astronomers rely on observations of the magnetic fingerprint left on light passing through the field. This imprint is also known as Faraday rotation.

The astronomers discovered a quasar — an incredibly bright galactic core powered by a supermassive black hole — located beyond the galaxy being studied, along the same line of sight. As the bright light from the quasar passes through the galaxy’s magnetic field, it picks up the Faraday rotation fingerprint, providing astronomers with the information they need to learn more about the field’s strength and direction, the researchers said. 

“Nobody knows where cosmic magnetism comes from or how it was generated,” Gaensler said in the statement. “But now, we have obtained a major clue needed for solving this mystery, by extracting the fossil record of magnetism in a galaxy billions of years before the present day.”

Their findings were published today (Aug. 28) in the journal Nature Astronomy.


Do Medium-Size Black Holes Exist

July 7, 2017 by  
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For decades, while astronomers have detected black holes equal in mass either to a few suns or millions of suns, the missing-link black holes in between have eluded discovery. Now, a new study suggests such intermediate-mass black holes may not exist in the modern-day universe because of the rate at which black holes grow.

Scientists think stellar-mass black holes — up to a few times the sun’s mass — form when giant stars die and collapse in on themselves. Over the years, astronomers have detected a number of stellar-mass black holes in the nearby universe, and in 2010, researchers detected the first such black hole outside the local cluster of nearby galaxies known as the Local Group.

As big as stellar-mass black holes might seem, they are tiny in comparison to the so-called supermassive black holes that are millions to billions of times the sun’s mass, which form the hearts of most, if not all, large galaxies. The oldest supermassive black holes found to date include one found in 2015 — with a mass of about 12 billion solar masses — that existed when the universe was only about 875 million years old. This finding and others suggest that many black holes were born in the dawn of time, back when the universe was smaller and matter was more concentrated, making it easier for them to form and grow.

Much remains uncertain about how black holes reach supermassive girth and influence the universe around them. As such, astronomers want to analyze intermediate-mass black holes of about 100 to 10,000 solar masses that they expect would serve as the middle stages between stellar-mass and supermassive black holes.

However, while astronomers have discovered a number of potential intermediate-mass black holes, the evidence remains inconclusive, said astrophysicists Tal Alexander at the Weizmann Institute of Science in Rehovot, Israel, and Ben Bar-Or at the Institute for Advanced Study in Princeton, New Jersey.

Now these researchers suggest the dearth of these missing links may be due to the rate at which black holes may grow. They detailed their findings online June 19 in the journal Nature Astronomy.

In recent years, scientists have discovered a dozen or so instances of black holes devouring stars. If black holes grew solely by consuming stars and dense, compact objects such as white dwarfs and neutrons stars instead of, say, giant clouds of gas or dark matter, the researchers estimated that black holes would still grow at the relatively constant rate of one solar mass per 10,000 years. (If they could eat gas or dark matter, they could grow even faster, but the data regarding such materials in the early universe is more open to question.)

Although one solar mass per 10,000 years may not seem especially quick, it means that even a stellar-mass black hole could grow completely past the intermediate-mass stage after 10 billion years. In comparison, the universe is about 13.8 billion years old.

These findings suggest that the seeds for supermassive black holes “were created quite early on in galaxies, when things were more dense,” Bar-Or told These seeds already exceeded intermediate-mass stage by about 1.6 billion to 2.2 billion years after the Big Bang — “some or even most of the black holes may have passed the supermassive-black-hole mass threshold even earlier,” Alexander told

Although the researchers said that intermediate-mass black holes may exist in the present day in dense areas such as globular clusters of stars, they remain difficult to identify because the light produced by objects falling into them is “not spectacular, and there are other objects that can produce it,” Alexander said.

Instead, “the ultimate way of finding and identifying intermediate-mass black holes is not by the emission of light, but by the emission of gravitational waves,” Alexander said. Gravitational waves are ripples in the fabric space and time, and the Evolved Laser Interferometer Space Antenna (ELISA) mission currently planned for 2034 could detect gravitational waves generated “when two intermediate-mass black holes coalesce together, Alexander said.


Astronomer Find The Building Blocks Of Life Found Around Baby Star

June 21, 2017 by  
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The young, triple-star system IRAS 16293-2422 is located approximately 400 light-years from Earth in the constellation of Ophiuchus. The infant stars in this system have a similar mass to the sun, but are still in the early stages of formation. 

Researchers have detected a complex organic molecule called methyl isocyanate near the stars. This is the first time that the molecule, which can be a precursor to life, has been found around sun-like protostars, according to a statement from the European Southern Observatory (ESO). [6 Most Likely Places for Alien Life in the Solar System]

Previously, astronomers found a simple form of sugar in the disk of gas and dust surrounding IRAS 16293-2422. The sugar, called glycolaldehyde, is linked to the formation of RNA, which is one of the building blocks of life. 

“This star system seems to keep on giving! Following the discovery of sugars, we’ve now found methyl isocyanate,” Niels Ligterink and Audrey Coutens, researchers at the Leiden Observatory in the Netherlands and University College London, respectively, said in the statement. “This family of organic molecules is involved in the synthesis of peptides and amino acids, which, in the form of proteins, are the biological basis for life as we know it.” Ligterink and Coutens make up one of two teams of astronomers who detected the new molecule; the findings are detailed in two studies that will be published in the Monthly Notices of the Royal Astronomical Society.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile, the astronomers found signatures of methyl isocyanate molecules in the inner regions of the dust and gas surrounding each of the stars, according to the ESO statement. “We are particularly excited about the result because these protostars are very similar to the sun at the beginning of its lifetime, with the sort of conditions that are well suited for Earth-sized planets to form,” Rafael Martín-Doménech and Víctor M. Rivilla, co-lead authors of the second study, said in the statement. “By finding prebiotic molecules in this study, we may now have another piece of the puzzle in understanding how life came about on our planet.”

Earth and other planets in the solar system formed from material left over after the formation of the sun. Therefore, studying young, sun-like stars like IRAS 16293-2422 can help astronomers learn more the early years of our solar system.

In addition to the ALMA data, both teams of researchers used computer chemical modeling to better understand the origin of the methyl isocyanate molecules.

Models suggest that the molecules likely formed on “icy particles under very cold conditions that are similar to those in interstellar space,” Ligterink said. 

“This implies that this molecule — and thus the basis for peptide bonds — is indeed likely to be present near most new young solar-type stars,” he added. 


Einstein’s Theory Used To Calculate The Mass Of A Star

June 16, 2017 by  
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The mass of Stein 2051 B, a white dwarf star located about 18 light-years from Earth, has been a subject of some controversy for over a century. Now, a group of astronomers has finally made a precise measurement of the star’s mass and settled a 100-year-old debate, using a cosmic phenomenon first predicted by Albert Einstein. 

The researchers calculated the star’s mass using carefully timed observations made by the Hubble Space Telescope, which studied Stein 2051 B when it eclipsed another, more distant star, as seen from Earth. During this transit, the background star appeared to change its position in the sky, moving ever so slightly to the side, even though its actual position on the sky had not changed at all. 

This cosmic optical illusion is broadly known as gravitational lensing, and its effects have been observed extensively throughout the universe, especially near very massive objects, such as entire galaxies. The effect occurs because a massive object warps the space around it and acts like a very large lens, bending the path of the light from the more distant object. In some cases, this creates the illusion that the background star has been displaced. 

(Water can also create this kind of displacement illusion; try placing a pencil in a glass of water, and note that the submerged half of the pencil appears disconnected from the dry half.)  

Einstein predicted that these displacement events could be used to measure individual stellar masses. That’s because the extent to which the background star’s position is offset depends on the mass of the foreground star. But telescopes at the time lacked the sensitivity to make that dream a reality. 

The scientists behind the new work said no one, before now, has ever used the displacement of a background star to calculate the mass of an individual star. In fact, there is only one other example of scientists measuring this displacement between individual stars: During the 1919 total solar eclipse, scientists saw the sun displace a few background stars. That measurement was possible only because of the sun’s proximity to Earth. 

A paper describing the new work was published online today in the journal Science.

Einstein’s theory of general relativity hypothesized that space is flexible rather than fixed, and that massive objects (like stars) create curves in space, sort of like a bowling ball creating a curve on the surface of a mattress. The degree to which an object warps space-time depends on how massive that object is (similarly, a heavier bowling ball puts a deeper imprint on a mattress).

A ray of light normally travels in a straight line through empty space, but if the ray passes close by a massive object, the curve in space created by the star acts like a bend in the road, causing the light ray to veer away from its formerly straight path. 

Einstein showed that this deflection could direct more light toward the observer, similar to how a magnifying glass can focus diffuse light from the sun down into a single spot. This effect causes the background object to appear brighter, or it creates a ring of bright light around the foreground object called an Einstein ring.  

Astronomers have observed Einstein rings and “brightening events” when very massive foreground lenses, like entire galaxies, create the phenomena. These have also been observed along the plane of the Milky Way galaxy, where individual stars likely cause the lensing effect. It has also been used to detect planets around other stars.  

In the new study, astronomers reported the first ever observation of so-called “asymmetric lensing” involving two stars outside Earth’s solar system, in which the position of the background star appeared to change. 

The degree of displacement is directly related to the foreground object’s mass. With relatively “light” objects, like stars, the displacement is extremely small and thus more difficult to detect, according to Kailash C. Sahu, an astronomer at the Space Telescope Science Institute in Baltimore, and the lead author on the new paper. In the case of Stein 2051 B, the displacement was about 2 milliarcseconds on the plane of the sky, or about equal to the width of a quarter seen from 1,500 miles (2,400 kilometers) away, Sahu said.

Measuring such a subtle change required a powerful instrument, like the Hubble telescope’s high-resolution camera, which was installed in 2009. This instrument also made it possible to pick out the light from the displaced star, which was somewhat overshadowed by the light from Stein 2051 B — like a firefly next to a lightbulb, Sahu said. 

The researchers took eight measurements between October 2013 and October 2015, so they could observe the white dwarf moving across the sky, eclipsing the background star and creating the displacement. The scientists also observed the actual position of the background star after the white dwarf had passed by. 

Many variables could affect whether scientists can observe more events like this. Those variables include the alignment of the two objects, the mass and proximity of the foreground object, the separation between the foreground and background object, and the sensitivity of the telescope. But Sahu said he thinks his team has demonstrated the effectiveness of the method and that scientists could use it to measure the masses of about two to four nearby stars per year. 

White dwarfs are stars that have stopped burning hydrogen in their cores and subsequently shed their outer layers. In each of these stars, the remaining mas has collapsed into a dense core known as a white dwarf. This collapse drives up the temperature on the surface of these objects, so they may burn hotter than “living” stars. 

“At least 97 percent of the stars in the sky, including the sun, will become or already are white dwarfs,” Terry Oswalt, a professor of engineering and physics at Embry-Riddle Aeronautical University in Daytona Beach, Florida, wrote in an accompanying Perspectives article in Science. “Because they are the fossils of all prior generations of stars, white dwarfs are key to sorting out the history and evolution of galaxies such as our own.”

The mass of Stein 2051 B has been “a source of controversy for over 100 years,” said Oswalt, who was not affiliated with the new research. 

The current picture that scientists have of white dwarfs suggests that the mass and radius of these objects reveals important information about how they formed, what they’re made of, and what kind of stars they formed from, according to Sahu. 

Previous measurements of the mass of Stein 2051 B suggested it was largely composed of iron, but that finding presented several problems based on accepted theories about white dwarf formation and stellar evolution, according to the research paper. For example, to form large amounts of iron, the star that would become Stein 2051 B would have to have been extremely massive, but the radius of Stein 2051 B suggests it formed from a star not much larger than the sun. 

If those measurements of Stein 2051’s mass were correct, it would have sent astrophysicists back to the drawing board to figure out how such an object could have formed. Sahu said astronomers realized their measurements of Stein 2051 B’s mass were probably incorrect, but they had no way to know for sure.  

Typically, the only way to measure the mass of a star is to observe how it interacts with another massive body. For example, in a binary system where two stars orbit each other, the heavier star will have a large influence on the motion of the lighter one, and by observing the two stars’ interaction over time, scientists can calculate more and more specific values for the stars’ masses. Stein 2051 B has a companion, but the two bodies orbit very far apart, so their influence on each other is minimal. 

The new result shows that Stein 2051 B is in fact a very normal white dwarf, and it fits in just fine with the accepted formation theory Sahu said. Its mass is about 0.68 times the mass of the sun, indicating it formed from a star about 2.3 times the mass of the sun, Sahu said. That’s compared to the previous measurement which placed the white dwarf’s mass at about 0.5 times the mass of the sun. Not very many white dwarfs have had both their masses and radii measured precisely, he added .

“It confirms white dwarf mass-radius relationship,” he said. “[Astrophysicists] have been using that theory, and it’s good to know it’s on solid footing.”


Can Companies Mine The Moon AT A Profit

May 25, 2017 by  
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The first-ever private mining operation on the moon is scheduled to kick off in 2020, when a landing craft sent by Florida-based Moon Express will ferry a single scoop of lunar dirt and rocks back to Earth.

Unlike the three governments that have led lunar missions — the United States, the Soviet Union, and China — the owners of this private firm have something history-making in mind for that little ball of extraterrestrial soil: They plan to sell it.

“It will instantly become the most valuable and scarcest material on Earth,” says Bob Richards, the CEO of Moon Express. “We’ll make some of it available to scientific research. But we also plan to commoditize it ourselves.”

Moon Express is gearing up to become the first company to ever transport a commercial asset from space back to Earth. But it’s not alone.

Several ambitious startups are busily developing plans to launch mining operations on both the moon and asteroids, with initial proof-of-concept missions set to kick off over the next few years and more robust operations within a decade. China is a key player, too, along with a tiny, unlikely European upstart: the Grand Duchy of Luxembourg.

Those seeking to conquer celestial commodity markets are beckoned by the glittering wealth that could await them in space.

“We believe that the first trillionaires will be made from space resources,” says Richards.

Exactly which minerals will drive those fortunes remains to be seen.

The moon holds significant amounts of a special type of a futuristic fuel source called helium-3 — enough, some say, to meet all of Earth’s power demand for thousands of years providing scientists can master the fusion power technology to utilize it.

A fortune could be made by anyone able to capture and exploit one of the mountain-sized asteroids made of platinum or other precious metals thought to be orbiting the sun, or deposits of rare earth elements on the moon.

Others point to the potential for zero-gravity construction of super-massive colonizing spacecraft and mammoth floating structures using raw materials sourced from asteroids.

Most, however, are focused on a resource that’s commonplace on Earth: water.

Water, space entrepreneurs say, will be the key space commodity for an economy expanding into the solar system — both because it can sustain life as drinking water and breathable air, and because it can be broken down into hydrogen and oxygen to make rocket fuel.

Sourcing water from space could, for example, turn the moon into a depot for more ambitious missions.

“Water is like the oil of the solar system,” said Richards. “The moon could become a gas station in the sky.”

In the near term, Moon Express is focused on providing relatively low-cost transport to the surface of the moon for commercial, private, academic, and government customers.

One client that’s already signed up is the moon-burial company Celestis, which offers to send cremated human remains to the surface of the moon for a starting price of $12,500.

In 2016 Moon Express became the first private company in history to receive permission from the US Federal Aviation Administration to travel beyond Earth’s orbit and land a craft on the moon.

The company is planning three lunar missions by the time it brings back the small scoop of lunar soil, between the size of a baseball and basketball, in 2020.

Selling part of that scoop to private interests — for example, as moon gems for jewelry for the ultra-rich — will set an important precedent. The international Outer Space Treaty of 1967 says no country can claim sovereignty over extraterrestrial territory. But in 2015 President Barack Obama signed a law granting private citizens the rights to resources recovered from space.

The company’s first mission, slated for this year, will be in part an attempt to win the Google Lunar XPrize. The competition offers $20 million to the first private company able to land a rover on the moon’s surface, travel 500 meters, and then broadcast hi-definition images back to Earth.

Another company fielding a team for the XPrize, which also plans to eventually tap moon water, is Japan’s ispace Inc.

In December, ispace signed a memorandum of understanding with Japan’s national space agency, JAXA, for the “mining, transport, and use of resources on the moon,” according to a company statement.

During an initial phase of operations, from 2018 through 2023, ispace will go prospecting on the moonscape, sending exploratory robots into lunar craters and caves to check for water. Production is planned to begin in 2024.

China is also eyeing moon resources — especially helium-3.

As an energy source, helium-3 is as alluring as it is elusive: a non-radioactive agent that wouldn’t produce dangerous waste. The isotope is released by the sun and carried through the cosmos on solar winds that are blocked by Earth’s atmosphere, but collect on the surface of the moon.

As a result, the moon is “so rich” in helium-3, it could “solve human beings’ energy demand for around 10,000 years at least,” a top Chinese scientific advisor to the country’s moon exploration program, Professor Ouyang Ziyuan, told the BBC.


One of the top proponents of lunar helium-3 is Harrison Schmitt, a geologist who walked on the moon during NASA’s Apollo 17 mission and wrote a 2006 book advocating lunar helium-3 mining called Return to the Moon.

Others, however, are deeply skeptical — even if the necessary fusion technology, which has long eluded researchers, is mastered.

“I do not see this as being an economic solution to Earth’s energy needs,” Ian Crawford of the Department of Earth and Planetary Sciences at Birkbeck College, University of London, said in an email. “The problem is that the abundance is very low, of the order 10 parts per billion by mass in even the most abundant regions.”

Another potentially attractive lunar resource is the platinum group of metals, including iridium, palladium and platinum, which have special qualities that make them highly useful in electronic devices. Such elements, rare on earth, are thought to be bountiful on the moon.

Richards of Moon Express said it’s too soon to specify the most valuable resource on the moon.

“It would be speculative and predictive to say which specific element is going to be the game-changer,” he said. “Pick your favorite spice.”

For now, he says, the key target is water — which, to be sure, can be found on frozen asteroids circling the sun as well.

Two US companies, Planetary Resources and Deep Space Industries, are leading the charge into asteroid mining, largely with the aim of providing resources that other types of space missions will need.

Rick Tumlinson, chairman of Deep Space Industries, said his company plans to land its first prospector on an asteroid by 2020.

The company will use tiny scouts to explore and study prospective targets. When a prime asteroid has been located, a larger robot will land on it, bite out a chunk, and then use solar power to evaporate and capture water from the sample.

“Water, we believe, is relatively easy to harvest from asteroid materials,” said Tumlinson.

If all goes according to plan, “by the middle-20s, we’d be producing serious quantities of resources,” he said.

Planetary Resources is also focused on water.

“You can concentrate that solar energy and heat up the surface of the asteroid and literally bake off the water in the same way you’d bake a clay pot,” says CEO Chris Lewicki.


Both Lewicki and Tumlinson also point to the potential for supplying building materials in space, which could allow for the construction of super-massive floating structures that would be ungainly to launch from Earth.

In space, “you can build these huge structures we see in movies and science fiction,” said Lewicki. “The resource that will allow us to do that is the metal that’s on asteroids. We can use technology like 3D printing. We can print up a structure in space that never has to hold itself up on Earth, never has to take a violent rocket ride.”

As billionaires Elon Musk and Jeff Bezos explore ideas for colonizing space and Mars, someone, advocates of space mining say, will need to provide the raw materials, water and fuel the colonizers will need.

And while space mining might sound like science fiction, serious backers with deep pockets are taking notice.

A total of $1.8 billion was invested in space ventures in 2015 — more than in the prior 15 years combined, according to the Tauri Group consultancy. More than 50 venture capital firms invested in space deals in 2015, the most of any year, the group found.

The tiny European nation of Luxembourg has invested 25 million euros in Planetary Resources, and collaborated on the development of Prospector-X, the first spacecraft from Deep Space Industries.

The moon, said Richards, is like Earth’s 8th continent, and it’s largely unexplored.

“We’re like early pioneers,” he said, “looking at a whole new world.”





Astronomers Find X-Ray Tsunami Rolling Through Galaxy Cluster

May 11, 2017 by  
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A wave of hot gas twice as wide as the Milky Way galaxy roils the nearby Perseus galaxy cluster, a new study indicates.

The wave, which measures 200,000 light-years across, likely formed billions of years ago, after a neighboring cluster clipped Perseus, researchers said. You can watch the monster wave roll in this awesome NASA video.

“The wave we’ve identified is associated with the flyby of a smaller cluster, which shows that the merger activity that produced these giant structures is still ongoing,” lead author Stephen Walker, of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.

Galaxy clusters are the largest gravitationally bound structures in the universe. For example, Perseus — which lies 240 million light-years away from Earth, in the constellation of the same name — spans a vast 11 million light-years.

Most of the observable matter within galaxy clusters is superheated gas that glows in X-ray wavelengths, study team members said. Observations by NASA’s Chandra X-ray Observatory and other instruments have revealed many interesting formations in Perseus’ glowing gas, including an odd, 200,000-light-year-long concave feature dubbed “the bay.”

The bay generates no emissions, so — unlike some other features in the massive gas field — its origins don’t trace back to activity of the supermassive black hole at the core of Perseus’ central galaxy, NGC 1275, study team members said. And the bay’s shape doesn’t match those predicted by computer models that simulate normal gas sloshing, the scientists added.

So, the researchers re-analyzed Chandra images of the bay, filtering them to highlight edges and other important details. Then, the scientists compared these enhanced observations to computer simulations of merging galaxy clusters performed by astrophysicist John ZuHone, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

“Galaxy cluster mergers represent the latest stage of structure formation in the cosmos,” said ZuHone, who’s not a member of the new study’s team. (His simulations are available to other researchers in an online catalog.)

“Hydrodynamic simulations of merging clusters allow us to produce features in the hot gas and tune physical parameters, such as the magnetic field,” ZuHone said in the same statement. “Then we can attempt to match the detailed characteristics of the structures we observe in X-rays.”

Such comparative work led the researchers to identify a likely birth scenario for the bay. Long ago, Perseus’ gas had settled into two separate components: an interior “cold” region with temperatures around 54 million degrees Fahrenheit (30 million degrees Celsius) and a surrounding area three times hotter, the idea goes.

Then, a smaller cluster about 1,000 times more massive than the Milky Way galaxy grazed Perseus, coming within 650,000 light-years or so of its core, researchers said. This near miss roiled Perseus’ gas significantly, generating a spiral that expanded outward from the “cold” interior region.

years after the cluster flyby, this spiral reached 500,000 light-years from Perseus’ center and began producing huge waves in the cluster’s outer reaches. These features are basically enormous versions of “Kelvin-Helmholtz waves,” which appear at the interface of two fluids that are moving at different velocities, the researchers said.

“We think the bay feature we see in Perseus is part of a Kelvin-Helmholtz wave, perhaps the largest one yet identified, that formed in much the same way as the simulation shows,” Walker said. “We have also identified similar features in two other galaxy clusters, Centaurus and Abell 1795.”

The new study will appear in the June 2017 issue of the journal Monthly Notices of the Royal Astronomical Society.


Astronomers Begin To Understand The Mystery Behind Merging Black Holes

April 20, 2017 by  
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Last year, scientists announced that they had finally observed gravitational waves, the elusive and long sought-after ripples in the fabric of spacetime that were first posited by Albert Einstein. The waves came from a catastrophic event — the collision of two black holes located about 1.3 billion light years away from Earth — and the released energy undulated across the universe, much like ripples in a pond.

The detection by the upgraded Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO), along with two subsequent gravitational wave discoveries, confirmed a major prediction of Einstein’s 1915 general theory of relativity and heralded a new era in physics, allowing scientists to study the universe in a new way by using gravity instead of light.

But a fundamental question remains unanswered: How and why do black holes collide and merge?

In order for the black holes to merge, they must start out very close together by astronomical standards, no more than about a fifth of the distance between the Earth and the Sun. But only stars with very large masses can become black holes, and during the course of their lives, these stars expand to become even larger.

A new study published in Nature Communications uses a model called COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) in an attempt to answer how large binary stars that would eventually become black holes fit within a very small orbit. COMPAS allows the researchers to pursue a kind of “paleontology” for gravitational waves.

“A paleontologist, who has never seen a living dinosaur, can figure out how the dinosaur looked and lived from its skeletal remains,” said Ilya Mandel from the University of Birmingham in the UK, the paper’s senior author, in a statement. “In a similar way, we can analyze the mergers of black holes, and use these observations to figure out how those stars interacted during their brief but intense lives.”

What they found was that even two widely separated “progenitor” stars can interact when they expand, engaging in several episodes of mass transfer.

The researchers started by analyzing the three gravitational wave events that were detected by LIGO and attempted to see if all three black hole collisions evolved in the same way, which they call “classical isolated binary evolution via a common-envelope phase.”

It starts with two massive progenitor stars at quite wide separations. As the stars expand, once they come so close that they cannot escape each other’s gravity, they begin to interact and engage in several episodes of mass transfer. This results in a very rapid, dynamically unstable event that envelops both stellar cores in a dense cloud of hydrogen gas.

“Ejecting this gas from the system takes energy away from the orbit,” the team said. “This brings the two stars sufficiently close together for gravitational-wave emission to be efficient, right at the time when they are small enough that such closeness will no longer put them into contact.”

It actually takes few million years to form two black holes, with a possible subsequent delay of billions of years before the black holes merge and form a single, larger black hole. But that merger event itself can be quick and violent.

The researchers said the simulations with COMPAS have also helped the team to understand the typical properties of the binary stars that can go on to form such pairs of merging black holes and the environments where this can happen.

For example, the team found that a merger of two black holes with significantly unequal masses would be a strong indication that the stars formed almost entirely from hydrogen and helium — called low-metallicity stars — with other elements contributing fewer than 0.1 percent of stellar matter (for comparison, this fraction is about 2 percent in our Sun). They were able to determine that all three events detected by LIGO could have formed in low-metallicity environments.

“The beauty of COMPAS is that it allows us to combine all of our observations and start piecing together the puzzle of how these black holes merge, sending these ripples in spacetime that we were able to observe at LIGO,” said Simon Stevenson, a Ph.D. candidate at the University of Birmingham and the paper’s lead author.

The team will continue to use COMPAS to gain a greater understanding how the binary black holes discovered by LIGO could have formed, and how future observations could tell us even more about the most catastrophic events in the universe.


Astronomers Begin Campaign To Photograph A Black Hole

April 18, 2017 by  
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The campaign to capture the first-ever image of a black hole has begun.

From today (April 5) through April 14, astronomers will use a system of radio telescopes around the world to peer at the gigantic black hole at the center of the Milky Way, a behemoth called Sagittarius A* (Sgr A*) that’s 4 million times more massive than the sun.

The researchers hope to photograph Sgr A*’s event horizon — the “point of no return” beyond which nothing, not even light, can escape. (The interior of a black hole can never be imaged, because light cannot make it out.) [The Strangest Black Holes in the Universe]

“These are the observations that will help us to sort through all the wild theories about black holes — and there are many wild theories,” Gopal Narayanan, an astronomy research professor at the University of Massachusetts Amherst, said in a statement. “With data from this project, we will understand things about black holes that we have never understood before.” 

The project, known as the Event Horizon Telescope (EHT), links up observatories in Hawaii, Arizona, California, Mexico, Chile, Spain and Antarctica to create the equivalent of a radio instrument the size of the entire Earth. Such a powerful tool is necessary to view the event horizon of Sgr A*, which lies 26,000 light-years from our planet, EHT team members said.

“That’s like trying to image a grapefruit on the surface of the moon,” Narayanan said.

During the current campaign, EHT is also eyeing the supermassive black hole at the core of the galaxy M87, which lies 53.5 million light-years from Earth. This monster black hole’s mass is about 6 billion times that of the sun, so its event horizon is larger than that of Sgr A*, Narayanan said.

These observations should help astronomers determine the mass, spin and other characteristics of supermassive black holes with better precision, team members said. The researchers also aim to learn more about how material accretes into disks around black holes, and the mechanics of the plasma jets that blast from these light-gobbling giants.

EHT could also reveal more about the “information paradox” — a long-standing puzzle about whether information about the material gobbled up by black holes can be destroyed — and other deep cosmological mysteries, team members said.

“At the very heart of Einstein’s general theory of relativity, there is a notion that quantum mechanics and general relativity can be melded, that there is a grand, unified theory of fundamental concepts,” Narayanan said. “The place to study that is at the event horizon of a black hole.”


Though the current observing campaign will be over soon, it will take a while for astronomers to piece together the images. For starters, so much information will be collected by the participating telescopes around the world that it will be physically flown, rather than transmitted, to the central processing facility at the Massachusetts Institute of Technology’s Haystack Observatory.

Then, the data will have to be calibrated to account for different weather, atmospheric and other conditions at the various sites. The first results from the campaign will likely be published next year, EHT team members said.


Are Astronomers About To Peek Inside A Black Hole?

April 6, 2017 by  
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Ever since first mentioned by Jon Michell in a letter to the Royal Society in 1783, black holes have captured the imagination of scientists, writers, filmmakers and other artists. Perhaps part of the allure is that these enigmatic objects have never actually been “seen.” But this could now be about to change as an international team of astronomers is connecting a number of telescopes on Earth in the hope of making the first ever image of a black hole.

Black holes are regions of space inside which the pull of gravity is so strong that nothing – not even light – can escape. Their existence was predicted mathematically by Karl Schwarzchild in 1915, as a solution to equations posed in Albert Einstein’s theory of general relativity.

Astronomers have had circumstantial evidence for many decades that supermassive black holes – a million to a billion times more massive than our sun – lie at the hearts of massive galaxies. That’s because they can see the gravitational pull they have on stars orbiting around the galactic centre. When overfed with material from the surrounding galactic environment, they also eject detectable plumes or jets of plasma to speeds close to that of light. Last year, the LIGO experiment provided even more proof by famously detecting ripples in space-time caused by two medium-mass black holes that merged millions of years ago.

But while we now know that black holes exist, questions regarding their origin, evolution and influence in the universe remain at the forefront of modern astronomy.

Catching a tiny spot on the sky

On April 5-14 2017, the team behind the Event Horizon Telescope hopes to test the fundamental theories of black-hole physics by attempting to take the first ever image of a black hole’s event horizon (the point at which theory predicts nothing can escape). By connecting a global array of radio telescopes together to form the equivalent of a giant Earth-sized telescope – using a technique known as Very Long Baseline Interferometry and Earth-aperture synthesis – scientists will peer into the heart of our Milky Way galaxy where a black hole that is 4m times more massive than our sun – Sagittarius A* – lurks.

Astronomers know there is a disk of dust and gas orbiting around the black hole. The path the light from this material takes will be distorted in the gravitational field of the black hole. Its brightness and colour are also expected to be altered in predictable ways. The tell-tale signature astronomers hope to see with the Event Horizon Telescope is a bright crescent shape rather than a disk. And they may even see the shadow of the black hole’s event horizon against the backdrop of this brightly shining swirling material.

The array connects nine stations spanning the globe – some individual telescopes, others collections of telescopes – in Antarctica, Chile, Hawaii, Spain, Mexico and Arizona. The “virtual telescope” has been in development for many years and the technology has been tested. However, these tests initially revealed a limited sensitivity and an angular resolution that was insufficient to probe down to the scales needed to reach the black hole. But the addition of sensitive new arrays of telescopes – including the Atacama Large Millimeter Array in Chile and the South Pole Telescope – will give the network a much-needed boost in power. It’s rather like putting on spectacles and suddenly being able to see both headlights from an oncoming car rather than a single blur of light.

The black hole is a compact source on the sky – its view at optical wavelengths (light that we can see) is completely blocked by large quantities of dust and gas. However, telescopes with sufficient resolution and operating at longer, radio millimetre wavelengths can peer through this cosmic fog.

The resolution of any kind of telescope – the finest detail that can be discerned and measured – is usually quoted as a small angle corresponding to the ratio of an object’s size to its distance. The angular size of the moon as seen from the Earth is about half a degree, or 1800 arc seconds. For any telescope, the bigger its aperture, the smaller the detail that can be resolved.

The resolution of a single radio telescope (typically with an aperture of 100 metres) is roughly about 60 arc seconds. This is comparable to the resolution of the unaided human eye and about a sixtieth of the apparent diameter of the full moon. But by connecting many telescopes, the Event Horizon Telescope will be about to achieve a resolution of 15-20 microarcsecond (0,000015 arcseconds), corresponding to being able to spy a grape at the distance of the moon.

What’s at stake?

Although the practice of connecting many telescopes in this way is well known, particular challenges lie ahead for the Event Horizon Telescope. The data recorded at each station in the network will be shipped to a central processing facility where a supercomputer will carefully combine all the data. Different weather, atmospheric and telescope conditions at each site will require meticulous calibration of the data so that scientists can be sure any features they find in the final images are not artefacts.

If it works, imaging the material inside the black hole region with angular resolutions comparable to that of its event horizon will open a new era of black hole studies and solve a number of big questions: do event horizons even exist? Does Einstein’s theory work in this region of extreme strong gravity or do we need a new theory to describe gravity this close to a black hole? Also, how are black holes fed and how is material ejected?

It may even even be possible to image the black holes at the center of nearby galaxies, such as the giant elliptical galaxy that lies at the heart of our local cluster of galaxies.

Ultimately, the combination of mathematical theory and deep physical insight, global international scientific collaborations and remarkable, tenacious long-term advances in cutting edge experimental physics and engineering look set to make revealing the nature of spacetime a defining feature of early 21st century science.


Astronomers Theroize The Growth Of Supermassive Black Holes

April 5, 2017 by  
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They grow up so fast: A new simulation shows how supermassive black holes could have gotten so large, so quickly in the early universe — by taking a shortcut via a star.

Supermassive black holes form the cores of many galaxies, including the Milky Way, and researchers have found evidence of them dating to very early in the universe’s history. In fact, seemingly too early — supermassive black holes take a long time to form, and researchers have been searching for explanations of how they were able to grow so massive (several billion times the sun’s mass) within the first billion years after the Big Bang, surpassing their apparent “speed limit” on growth.

According to a new simulation, black holes can only grow so fast, but stars can expand to incredible size even faster in certain conditions before collapsing down into a black hole. That way, the energetic galactic centers can form earlier than expected. The researchers also explained their simulation in a new video.

“It turns out that while supermassive black holes have a growth speed limit, certain types of massive stars do not,” Joseph Smidt, a researcher at the theoretical design division of Los Alamos National Laboratory and the first author on the new work, said in a statement. “We asked, what if we could find a place where stars could grow much faster, perhaps to the size of many thousand suns; could they form supermassive black holes in less time?”

The researchers compared their models to the most distant known energetic galactic center, called a quasar, and one of the most massive of those objects, which is also ancient, to see whether that method could have quickly grown them to full size. If ultralarge stars are born in the right environment — one with the ideal combination of rapidly incoming material and local conditions — they could indeed collapse and form quasars of that mass and age, the researchers found.

The simulation also ended up accurately modeling star formation and other phenomena that happen around black holes, the distribution of galaxy densities, gas temperature changes and ionization, the researchers said in the statement.

“This was largely unexpected,” Smidt said. “I thought this idea of growing a massive star in a special configuration and forming a black hole with the right kind of masses was something we could approximate, but to see the black hole inducing star formation and driving the dynamics in ways that we’ve observed in nature was really the icing on the cake.”

The new work has been submitted to The Astrophysical Journal, and it is currently available online at


Astronomers Find Runaway Star Siblings

March 30, 2017 by  
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Researchers have spotted a long-lost relative of two runaway stars — the three likely parted ways in the Orion nebula as recently as the 1400s (from Earth’s perspective).

Two of the young stars were previously discovered speeding away from one another using radio and infrared observations, and observers had traced back to where they could have originated if they’d been from the same system initially. But something didn’t quite add up: the two seemed to not have as much combined energy as expected, suggesting that there might be at least one more star that was involved in the system’s breakup.

Now, astronomers think they’ve found the third — another runaway star that came from that same spot in the star-forming region 540 years ago, pinpointed in images from the Hubble Space Telescope.

“The new Hubble observations provide very strong evidence that the three stars were ejected from a multiple-star system,” the new work’s lead researcher, Kevin Luhman of Penn State University, said in a statement. “Astronomers had previously found a few other examples of fast-moving stars that trace back to multiple-star systems, and therefore were likely ejected. But these three stars are the youngest examples of such ejected stars.”

“They’re probably only a few hundred thousand years old,” Luhman added. “In fact, based on infrared images, the stars are still young enough to have disks of material leftover from their formation.”

The three stars are all in a region full of young stars called the Kleinmann-Low nebula, which is embedded in the Orion nebula 1,300 light-years away. Each is moving at top speeds of almost 30 times the speed of most of the nebula’s stars, researchers said in the statement, and the nebula’s thick shroud of dust hides them from most observers (often only radio waves, and sometimes infrared radiation, that the stars produce can make it through the dust).

Luhmann found the star while hunting for free-floating planets on a research team at the Space Telescope Science Institute in Maryland. He was looking at near-infrared data from Hubble’s Wide Field Camera 3, and noticed that one glowing spot had changed position in between 1998 and 2015 as compared to nearby stars — suggesting it was moving at about 130,000 mph (210,000 kph), according to the statement. 

Working backward, he found that it could have originated in the same spot as the other two runaways. He projected that two members of the multiple-star system approached close enough to merge or form a close binary, unleashing the gravitational energy to fling all the stars outward. (The other two stars are moving away from the origin point at 60,000 mph, or 97,000 kph, and 22,000 mph, or 35,000 kph, respectively.)

According to simulations, such interactions should happen often in crowded clusters of young stars.

“But we haven’t observed many examples, especially in very young clusters,” Luhman said. “The Orion Nebula could be surrounded by additional fledgling stars that were ejected from it in the past and are now streaming away into space.”


Monster Galaxy Cluster Sheds Light On Cosmic Microwave Background

March 28, 2017 by  
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One of the largest galaxy clusters ever seen shines bright in this image from the Hubble Space Telescope. Called RX J1347.5-1145, this cluster lies 5 billion light-years from Earth.

Hubble’s observations of this galaxy cluster helped astronomers at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to probe the secrets of the cosmos by watching how it interacts with the cosmic microwave background (CMB) — weak radiation left over from the Big Bang, when the universe as we know it was born.

The entire cosmos bears witness to the disruptive events surrounding the Big Bang. Marks left behind by the rapid expansion of space-time can be found by studying the universe’s most ancient light, the CMB. These 14 billion-year-old photons, or particles of light, now permeate the cosmos and can be used to learn about the universe via a phenomenon known as the Sunyaev-Zel’dovich effect.

Microwave radiation is invisible to the human eye, but astronomers can detect it. The microwave photons that create the CMB travel through the universe to Earth. “On their journey to us, they can pass through galaxy clusters that contain high-energy electrons,” NASA officials said in a statement. Passing through areas containing high-energy electrons can give these ancient photons get a little energy boost.

“Detecting these boosted photons through our telescopes is challenging but important,” NASA officials said. “They can help astronomers to understand some of the fundamental properties of the universe, such as the location and distribution of dense galaxy clusters.”

After ALMA observed the CMB around the galaxy cluster RX J1347.5-1145 (shown in blue), astronomers combined that data with an image from the Cluster Lensing and Supernova survey with Hubble (CLASH) to make this picture. Combining the visible-light image from Hubble with the invisible microwave data from ALMA helps astronomers understand how the CMB interacts with the galaxies inside the colossal cluster.


Can Black Holes Rapidly Change Their Temperature?

March 10, 2017 by  
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Supermassive black holes are thought to be embedded in the middle of most large galaxies, including the Milky Way. These monsters feed from a surrounding disk of gas, dust and other material, called an accretion disk. The gravitational pull of the black hole can heat up material in the accretion disk, causing it to radiate light.

Young and energetic black holes can gobble up only so much material, however, before the feeding process produces hot streams of gas from the accretion disk. These black-hole winds travel at about a quarter of the speed of light, and have the potential to disturb star formation in their wake

Using NuSTAR and the European Space Agency’s XMM-Newton telescope, scientists have for the first time observed winds from a nearby black hole interacting with radiation coming from the black hole’s edge, according to the authors of a study.

Harrison’s team wanted to learn about the temperatures of these winds, so they looked at X-rays coming from the black hole’s edge. As the X-rays pass through the winds, chemical elements present in the winds — such as iron and magnesium — absorb some wavelengths of light in the X-ray spectrum. The spectrum then displays holes, also called “absorption features,” revealing more about the wind’s composition.

“While observing this spectrum, the team noticed that the absorption features were disappearing and reappearing in the span of a few hours,” according to a statement from the California Institute of Technology (Caltech). “The team concluded that the X-rays were actually heating up the winds to very high temperatures — millions of degrees Fahrenheit — such that they became incapable of absorbing any more X-rays. The winds then cool off, and the absorption features return, starting the cycle over again.”

Being able to study the properties of these winds offers scientists an opportunity to learn more about how those winds impact the evolution of galaxies.

“We know that supermassive black holes affect the environment of their host galaxies, and powerful winds arising from near the black hole may be one means for them to do so,” Fiona Harrison, NuSTAR principal investigator and a physics and astronomy professor at Caltech, said in the statement. “The rapid variability, observed for the first time, is providing clues as to how these winds form, and how much energy they may carry out into the galaxy.”

The researchers are planning to conduct more observations to learn how the winds are formed, where their source of power is from and how long they last, among other features. The findings will be published tomorrow (March 2) in the journal Nature.


Astronomers Find The Building Blocks Of Life On Ceres

February 23, 2017 by  
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The dwarf planet Ceres keeps looking better and better as a possible home for alien life.

NASA’s Dawn spacecraft has spotted organic molecules — the carbon-containing building blocks of life as we know it — on Ceres for the first time, a study published today (Feb. 16) in the journal Science reports.

And these organics appear to be native, likely forming on Ceres rather than arriving via asteroid or comet strikes, study team members said.

“Because Ceres is a dwarf planet that may still preserve internal heat from its formation period and may even contain a subsurface ocean, this opens the possibility that primitive life could have developed on Ceres itself,” Michael Küppers, a planetary scientist based at the European Space Astronomy Centre just outside Madrid, said in an accompanying “News and Views” article in the same issue of Science.

“It joins Mars and several satellites of the giant planets in the list of locations in the solar system that may harbor life,” added Küppers, who was not involved in the organics discovery.

The $467 million Dawn mission launched in September 2007 to study Vesta and Ceres, the two largest objects in the main asteroid belt between Mars and Jupiter. 

Dawn circled the 330-mile-wide (530 kilometers) Vesta from July 2011 through September 2012, when it departed for Ceres, which is 590 miles (950 km) across. Dawn arrived at the dwarf planet in March 2015, becoming the first spacecraft ever to orbit two different bodies beyond the Earth-moon system.

During its time at Ceres, Dawn has found bizarre bright spots on crater floors, discovered a likely ice volcano 2.5 miles (4 km) tall and helped scientists determine that water ice is common just beneath the surface, especially near the dwarf planet’s poles.

The newly announced organics discovery adds to this list of achievements. The carbon-containing molecules — which Dawn spotted using its visible and infrared mapping spectrometer instrument — are concentrated in a 385-square-mile (1,000 square km) area near Ceres’ 33-mile-wide (53 km) Ernutet crater, though there’s also a much smaller patch about 250 miles (400 km) away, in a crater called Inamahari. 

And there could be more such areas; the team surveyed only Ceres’ middle latitudes, between 60 degrees north and 60 degrees south. 

“We cannot exclude that there are other locations rich in organics not sampled by the survey, or below the detection limit,” study lead author Maria Cristina De Sanctis, of the Institute for Space Astrophysics and Space Planetology in Rome, told via email.

Dawn’s measurements aren’t precise enough to nail down exactly what the newfound organics are, but their signatures are consistent with tar-like substances such as kerite and asphaltite, study team members said.

“The organic-rich areas include carbonate and ammoniated species, which are clearly Ceres’ endogenous material, making it unlikely that the organics arrived via an external impactor,” co-author Simone Marchi, a senior research scientist at the Southwest Research Institute in Boulder, Colorado, said in a statement. 

In addition, the intense heat generated by an asteroid or comet strike likely would have destroyed the organics, further suggesting that the molecules are native to Ceres, study team members said.

The organics might have formed via reactions involving hot water, De Sanctis and her colleagues said. Indeed, “Ceres shows clear signatures of pervasive hydrothermal activity and aqueous alteration,” they wrote in the new study.

Such activity likely would have taken place underground. Dawn mission scientists aren’t sure yet how organics generated in the interior could make it up to the surface and leave the signatures observed by the spacecraft.

“The geological and morphological settings of Ernutet are still under investigation with the high-resolution data acquired in the last months, and we do not have a definitive answer for why Ernutet is so special,” De Sanctis said.

It’s already clear, however, that Ceres is a complex and intriguing world — one that astrobiologists are getting more and more excited about.

“In some ways, it is very similar to Europa and Enceladus,” De Sanctis said, referring to ocean-harboring moons of Jupiter and Saturn, respectively. 

“We see compounds on the surface of Ceres like the ones detected in the plume of Enceladus,” she added. “Ceres’ surface can be considered warmer with respect to the Saturnian and Jovian satellites, due to [its] distance from the sun. However, we do not have evidence of a subsurface ocean now on Ceres, but there are hints of subsurface recent fluids.” 


Astronomers Find Black Hole In Globular Cluster

February 15, 2017 by  
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For decades, astronomers have tracked black holes with masses millions of times that of the sun, as well as those with tens of solar masses. But black holes between those two extremes have proved elusive. Now, astronomers studying a globular cluster have found just such a black hole at its center, showing that intermediate-mass black holes could be hiding out in these compact agglomerations of stars.

Lead study author Bülent Kiziltan, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and his co-authors Holger Baumgardt (of Australia’s University of Queensland) and Abraham Loeb (also of CfA) found a black hole between 1,400 and 3,700 solar masses at the center of 47 Tucanae, a globular cluster in the southern sky some 16,700 light-years from Earth.

Black holes are usually found because they emit massive amounts of X-rays as matter falls in. Midsize black-hole candidates have been found in galaxies; a group from the University of Maryland and NASA’s Goddard Space Flight Center found one in another galaxy in 2015, and there are about a dozen objects in total. 

Kiziltan and his team found this one by measuring motions of pulsars within the cluster. They found the telltale signs of a compact, massive object in the cluster’s heart. The likeliest explanation for the motions was a black hole.

“Intermediate-mass black holes have been expected [in globular clusters] for many decades,” Kiziltan told “But we’ve not been able to find one conclusively.”

Theorists think stellar-mass black holes form from stars that are at least a few dozen times the mass of the sun. When they run out of nuclear fuel, there is no longer enough energy from radiation to hold the star’s outer layers against its immense gravity. The star collapses, and then explodes as a supernova. (Supernovas can outshine the galaxies in which they reside.) What’s left of the star then shrinks into a tiny volume. A 100-solar-mass star, as a black hole, would have a radius of about 180 miles (290 kilometers). The former star’s escape velocity exceeds that of light, resulting in a black hole, from which nothing can escape.

A big question for astronomers is what the population of black holes looks like. Given that there are supermassive black holes, and stellar-mass ones, there should be a population of black holes with masses between those two. But there don’t seem to be as many as expected. The centers of globular clusters, which are agglomerations of old stars, seemed a good place to look, as earlier studies indicated they might be there, according to the new study. 

The problem is, black holes are visible only when stuff falls in them. As such, the researchers needed another method that didn’t depend on picking up radio emissions.

That’s why Kiziltan and his colleagues decided to look at the pulsars that inhabit a globular cluster. Pulsars form from stars less massive than those that make black holes. After those stars go supernova, they collapse into neutron stars

Some neutron stars spin rapidly and emit radio waves along a line offset from their rotational axes. These are called pulsars. Earthbound observers see them if Earth is in the radio beam as it sweeps across the sky. Pulsars’ rotation rates change so little that they are precise timekeepers. They are precise enough that by timing the signal and looking for any Doppler shifts, it’s possible to measure a pulsar’s movement along one’s line of sight.

Kiziltan’s group tracked the movement of some two dozen pulsars and used computer simulations to model the cluster to track down their black-hole candidate.

“We’re proposing a brand-new approach to the study of globular clusters,” Kiziltan said. “It’s not only that we see the dynamical signature of a black hole, but how to probe the region near it without going too close to it.” Probing the centers of globular clusters is usually difficult, because the density of stars makes it hard to see what’s going on.

Finding the intermediate-mass black hole raises more questions about how these black holes form, said Cole Miller, a professor of astronomy at the University of Maryland who studies black-hole formation. “Let’s say it’s an intermediate-mass black hole,” he said. “How did it get there?”

“Globular clusters have small escape speeds,” he said. “So the stars should blow away all the gas.” There will be some as stars age, such as a red giant’s stellar winds. “But that amount of gas is nowhere close enough to make an intermediate-mass black hole.”

This differs from the supermassive black holes at galactic centers, he added, because one would expect lots of matter to accumulate there, feeding a black hole and allowing it to grow very fast.

Both Kiziltan and Cole said there are several ways to grow black holes early in a cluster’s history. “One of my favorites is runaway collisions of stars or stellar- mass black holes,” Miller said. “An interesting effect is, if you have a bunch of stars in a dense stellar region, the heaviest will start runaway collisions.” Once a black hole forms — perhaps when a star that’s absorbed a few neighbors dies ―  all the matter that isn’t in a stable orbit around the black hole will fall in or get ejected from the cluster, he said. That puts an automatic stop on the black hole’s growth.

For scientists to get a better handle on how such black holes might form in clusters, more of them need to be found — but that won’t be easy, Kiziltan said. The only reason it worked for 47 Tucanae was that there were enough pulsars in it to begin with, and they were close enough to see. Not every globular cluster has the right combination of distance and bright pulsars.


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