For the first time, astronomers have directly measured how fast a black hole spins, clocking its rotation at nearly half the speed of light.
The distant supermassive black hole would ordinarily be too faint to measure, but a rare lineup with a massive elliptical galaxy created a natural telescope known as a gravitational lens that allowed scientists to study the faraway object.
“The gravitational lens is crucial,” study co-author Mark Reynolds of the University of Michigan told Space.com via email..”Without this, we would not be able to collect X-ray photons to measure the spin of a black hole that is so distant.”
Nature’s free telescope
Just more than 6 billion light-years from Earth, a supermassive black hole powers the quasar . Quasars, the most luminous objects in the universe, shine brightly across vast distances, fed by material that falls into their black holes.
Black holes are massive objects whose gravitational pull is so powerful that even light cannot escape their grasp. Most form when a star at the end of its lifetime explodes, its outer core collapsing into a tiny dense ball.
Supermassive black holes have masses millions of times that of the sun and are found at the center of most galaxies, including the Milky Way. Their origins are still unknown.
The only features scientists are able to measure about the voracious objects are their mass and spin. Astronomers can determine the mass of a black hole by measuring its interactions with gas and other objects, but characterizing its rotation has remained a challenge, especially for more distant supermassive black holes.
In the new study, a team led by Rubens Reis of the University of Michigan used NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton — the largest X-ray space telescopes currently available — to observe the X-rays generated in the innermost regions of the disk of material circling and feeding the supermassive black hole that powers the quasar J1131.
Measuring the radius of the disk allowed the astronomers to calculate the black hole’s spin speed, which was almost half the speed of light.
The team would have been unable to measure the spin without a rare lineup in space. A giant elliptical galaxy lies between Earth and the quasar J1131. The huge galaxy acts as a gravitational lens to bend and magnify objects that lie behind it — in this case, the supermassive black hole.
“It acts like a telescope, but a free one provided by nature,” Reynolds said.
“Such a quadruple lens of a quasar is a very rare object,” Guido Risaliti, of the Harvard-Smithsonian Center for Astrophysics, told Space.com in an email. “Until a few years ago, none of them was known.”
Risaliti, who was not involved in the research, also studies supermassive black holes. Last year, he made the first reliable measurement of the spin of a nearby supermassive black hole. He authored a News & Views article that appeared along with the research in the journal Nature today (March 5). [No Escape: Dive Into a Black Hole (Infographic)]
The spin of a supermassive black hole can reveal information about how it accretes the material it consumes. To achieve a rapid spin, material must fall into the black hole in a direction similar to its rotation, ultimately revving it up like a child spinning a merry-go-round.
A slower spin indicates that the gas and dust supplying the black hole fall into it from multiple directions, spinning the black hole up or down depending on whether it comes in with or against the rotation. In this case, the random influx of material acts like a child alternating pushing and pulling the merry-go-round.
The quick spin of J1131 indicates that the black hole is being fed by a bountiful supply of gas and dust. These large volumes could be provided by collisions and mergers between galaxies, among other sources, Reynolds said.
A slower spin and more haphazard feeding process would be caused by material arriving in spurts, from interstellar gas clouds and stars wandering too close from a variety of directions.
“Observational studies over the past 20 years have shown a clear link between the mass of the supermassive black hole at the center of a galaxy and the properties of the galaxy in which it resides,” Reynolds said. “These relations suggest a symbiotic relationship between the central black hole and its host galaxy.”
By studying the black hole, astronomers can learn more about the origin and evolution of galaxies — and spin plays a very important role.
“The growth history of a supermassive black hole is encoded in its spin,” Reynolds said.
High spin values throughout most black holes would suggest that galaxy mergers have played a significant role in galactic evolution throughout the life of the universe. Determining how common rapid spin rates are will require the study of multiple distant supermassive black holes that lie in the active galactic nuclei (AGN) of nearby galaxies.
“The next immediate step is to obtain a few more black hole spins in the nearby AGN, but it will be difficult to repeat observations like the one of Reis’ team due to the rarity of these sources,” Risaliti said. “The big step forward will be the measurements of the black hole spins with the next generation of high sensitivity X-ray telescopes, such as the ESA’s Athena.”
In-pouring rivers of hydrogen gas could explain how spiral galaxies maintain the constant star formation that dominates their hearts, a new study reports.
Using the Green Bank Telescope (GBT) in West Virginia, scientists observed a tenuous filament of gas streaming into the galaxy NGC 6946, known as the “Fireworks Galaxy” because of the large number of supernovae observed within it. The find may provide insight into the source of fuel that powers the ongoing birth of young stars, researchers said.
“We knew that the fuel for star formation had to come from somewhere,” study lead author D.J. Pisano, of West Virginia University, said in a statement. “So far, however, we’ve detected only about 10 percent of what would be necessary to explain what we observe in many galaxies.”
Located 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, NGC 6946 is a medium-sized spiral galaxy pointed face-on toward the Milky Way.
Previous studies revealed a halo of hydrogen gas around NGC 6946 common to spiral galaxies. Such halos are formed by hydrogen ejected from the galaxies by star formation and violent supernova explosions. These interactions heat the gas in the halo to extreme temperatures.
When Pisano turned the GBT toward the spiral galaxy for further examination, however, he discovered a ribbon of gastoo cool to have suffered the heating processes undergone by halo gas.
On average, the Milky Way churns out between 1 to 5 new stars per year. Rich in gas, NGC 6946 is far more active. For example, it has hosted at least 9 explosive supernovae in the past century.
“Starburst” galaxies are even more prolific. These productive galaxiesshould have burned through the gas they were born with over the course of their lifetimes, bringing star formation to a sudden halt. Instead, the process continues today, suggesting that something is continuing to supply them with sufficient gas to keep creating more stars.
“A leading theory is that rivers of hydrogen — known as cold flows — may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation,” Pisano said. “But this tenuous hydrogen has simply been too diffuse to detect, until now.”
The immense, unblocked dish of the Green Bank Telescope, combined with its location in the National Radio Quiet Zone, where radio transmissions are limited, allow the large disk to detect the faint hydrogen signal that would be present in a cold flow.
Another possibility is that the hydrogen detected originated from a close encounter with another galaxy in the past. The gravitational interaction between the two could have stretched out a ribbon of neutral atomic hydrogen, researchers said. Such a ribbon would contain stars that astronomers should be able to easily observe, though none have yet been spotted. Further studies of the streamer hydrogen gas will help clarify its role.
After decades of wondering why young massive stars don’t blow away the gas surrounding them, astronomers have finally found a process that explains how these stellar youngsters hang on to their gassy envelopes.
This star type — more than 10 times the mass of the sun and most active in ultraviolet light — begins shining as a gigantic gas cloud collapses, fusing hydrogen into helium and igniting the star’s nuclear engine. The new research shows that this gas accretion continues even as the star shines, counteracting the stellar radiation that “pushes” against the gas.
A new model reveals that the gas falls unevenly onto the star and also clumps into spiral “filamentary concentrations” because there is so much gas in a small area. When the star moves through the spirals, these filaments absorb the ultraviolet radiation the star emits, protecting the surrounding gas. Once the absorption stops, the gas nebulas shrink. [Top 10 Star Mysteries]
“These transitions from rarefied to dense gas and back again occur quickly compared to most astronomical events,” Mac Low, a curator in the American Museum of Natural History’s Department of Astrophysics and co-author of the paper, said in a statement. “We predicted that measurable changes could occur over times as short as a few decades.”
Massive stars only influential not only when they are alive but also when they die. When a star of this size finishes burning the elements inside it, this triggers a massive collapse and explosion known as a supernova. These explosions created all elements in the universe that are heavier than iron, making Earth and other rocky planets possible.
Young massive stars have been closely studied for decades. Nobody could figure out why the gas around them didn’t blow away, however, as simpler models used previously implied that the gas would expand and dissipate.
The new models, based on observations from the Karl G. Jansky Very Large Array (VLA) in New Mexico, suggest that there are many small ionized hydrogen regions around these stars. The accretion process on the star kept going even after the hydrogen hotspots had formed, which was the opposite of what astronomers expected. Using models, astronomers then supposed that the gas falls unevenly on the star, creating the filaments.
Researchers came to this conclusion after using VLA observations of Sagittarius B2, a huge gas and dust cloud almost 400 light-years away from the center of the Milky Way galaxy. Between observations made in 1989 and 2012, researchers spotted four ionized hydrogen or HII regions getting brighter.
“The long-term trend is still the same, that HII regions expand with time,” said study leader Christopher De Pree, an astronomer at Agnes Scott College. “But in detail, they get brighter or get fainter and then recover. Careful measurements over time can observe this more detailed process.”
The research was recently published in Astrophysical Journal Letters and is also available in preprint form on Arxiv.
For the first time, astronomers have precisely calculated the rotation rate of a galaxy by measuring the tiny movements of its constituent stars.
Observations by NASA’s Hubble Space Telescope reveal that the central part of the nearby Large Magellanic Cloud galaxy (LMC) completes one rotation every 250 million years — coincidentally, the same amount of time it takes the sun finish a lap around the core of our own Milky Way.
“Studying this nearby galaxy by tracking the stars’ movements gives us a better understanding of the internal structure of disk galaxies,” study co-author Nitya Kallivayalil, of the University of Virginia, said in a statement today (Feb. 18). “Knowing a galaxy’s rotation rate offers insight into how a galaxy formed, and it can be used to calculate its mass.”
The Large Magellanic Cloud is one of the Milky Way’s nearest neighbors, located just 170,000 light-years away. The LMC has a central bar but an irregular shape, suggesting that it was once a Milky Way-like spiral that has been bent out of shape by gravitational interactions.
In the new study, the research team used Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys to measure the motion of hundreds of LMC stars over a seven-year period. Hubble is the only instrument precise enough to make such observations, scientists said.
“This precision is crucial, because the apparent stellar motions are so small because of the galaxy’s distance,” lead author Roeland van der Marel, of the Space Telescope Science Institute in Baltimore, said in a statement. “You can think of the LMC as a clock in the sky, on which the hands take 250 million years to make one revolution. We know the clock’s hands move, but even with Hubble we need to stare at them for several years to see any movement.”
The new Hubble data complement previous observations of the LMC, which estimated the galaxy’s rotation rate by measuring shifts in the spectrum of its starlight, researchers said. (The light from stars moving toward Earth shifts slightly toward the blue end of the spectrum, while that from stars receding from our planet appears redder.)
The LMC is an attractive target for astronomers interested in galactic structure and evolution, since it’s close enough to observe in detail but far enough away to take in completely.
“The LMC is a very important galaxy because it is very near to our Milky Way,” van der Marel said. “Studying the Milky Way is very hard because everything you see is spread all over the sky. It’s all at different distances, and you’re sitting in the middle of it. Studying structure and rotation is much easier if you view a nearby galaxy from the outside.”
Astronomers have found what appears to be one of the oldest known stars in the universe.
The ancient star formed not long after the Big Bang 13.8 billion years ago, according to Australia National University scientists. The star (called SMSS J031300.362670839.3) is located 6,000 light-years from Earth and formed from the remains of a primordial star that was 60 times more massive than the sun.
“This is the first time that we’ve been able to unambiguously say that we’ve found the chemical fingerprint of a first star,” lead scientist Stefan Keller, of the ANU Research School of Astronomy and Astrophysics, said in a statement. “This is one of the first steps in understanding what those first stars were like. What this star has enabled us to do is record the fingerprint of those first stars.” [See amazing photos of supernova explosions]
Scientists think SMSS J031300.362670839.3 is probably at least 13 billion years old, though they do not know its exact age, Anna Frebel, an MIT astronomer associated with the research, said
Keller and his team found that the star actually has an unexpected composition. Astronomers thought that primordial stars — like the one that SMSS J031300.362670839.3 formed from — died in huge supernova explosions that spread large amounts of iron throughout space.
However, the new observations have shown that SMSS J031300.362670839.3′s composition harbors no iron pollution. Instead, the star is mostly polluted by lighter elements like carbon, ANU officials said.
“This indicates the primordial star’s supernova explosion was of surprisingly low energy,” Keller said. “Although sufficient to disintegrate the primordial star, almost all of the heavy elements such as iron, were consumed by a black hole that formed at the heart of the explosion.”
The scientists also found that the early star’s composition is very different from the sun.
“To make a star like our sun, you take the basic ingredients of hydrogen and helium from the Big Bang and add an enormous amount of iron — the equivalent of about 1,000 times the Earth’s mass,” Keller said. “To make this ancient star, you need no more than an Australia-sized asteroid of iron and lots of carbon. It’s a very different recipe that tells us a lot about the nature of the first stars and how they died.”
Because of its low mass, the star, located in the Milky Way, has a long lifetime, Anna Frebel, an MIT astronomer associated with the research, told Space.com via email.
Keller and his team found SMSS J031300.362670839.3 by using the ANU SkyMapper telescope. SkyMapper is surveying the sky at the Siding Spring Observatory in Australia to produce the first-ever digital map of the sky in the Southern Hemisphere. They confirmed their observations using the Magellan telescope in Chile.
Black holes acting as companions to early stars may have taken more time to raise the temperature of the ancient universe than previously thought, a new study suggests.
Scientists found that the energy streaming from these early pairings took longer to raise the temperature of the universe, which means astronomers could detect signs of the heating process previously thought to be out of bounds. Two cosmic milestones occurred in the universe a few hundred million years after the Big Bang— dominating hydrogen gas was both heated and made transparent.
“Previously, it was thought that these two milestones are well separated in time, and thus in observational data as well,” study co-author Rennan Barkana, of Tel Aviv University, told Space.com via email. [The History and Structure of the Universe (Infographic Slideshow)]
Barkana worked with lead study author Anastasia Fialkov, also of Tel Aviv University, and Eli Visbal, of Columbia University, to determine that the heating most likely overlapped the early, and perhaps middle, part of reionization, the process that allowed the events of the early universe to become visible to scientists today, making the heating potentially observable to astronomers today.
High energy, low heat
Like stars today, stars in the early universe often had companions. When one of the two companion stars exploded to create a black hole, the new system — known as an X-ray binary (XRB) — emitted energy in the X-ray spectra. Although other systems emit X-rays, XRBs are the brightest, dominating the total cosmic intensity of X-rays.
In the early universe, energetic X-rays served to heat the hydrogen gas that filled space. Previously, scientists suspected that low-energy X-rays provided the energy to heat the early universe. But recent improved models of XRBs revealed that high-energy X-rays dominated the scene.
Fialkov’s team used new models to recalculate the amount of time required to increase the temperature of the hydrogen spread throughout the universe. Surprisingly, the researchers said, the higher-energy X-rays took longer to raise temperatures than the less-powerful rays.
“High-energy X-rays typically travel a long distance, over a long time, before their energy is absorbed and heats the gas,” Barkana said. “Eventually, all their energy is deposited, but ‘eventually’ is too late in the early universe, when galaxy and star formation are ramping up.”
After the Big Bang, protons and neutrons joined together to form neutral hydrogen, the most basic element on the periodic table and the dominate gas in the universe. The dominance of neutral hydrogen rendered the universe opaque, in a period known as the cosmic ‘Dark Ages’ that existed during the first 100 million years after the Big Bang. Only after stars and galaxies began to form and release ultraviolet light did the universe begin the process of reionization, clearing the hydrogen gas and making the universe once again transparent.
The early stars didn’t manage to clear the darkness of the early universe until nearly a billion years had passed since the Big Bang. As a result, astronomers cannot peer through the darkness to observe the first billion years in the life of the 13.8-billion-year-old universe.
With low-energy X-rays dominating the scene, hydrogen gas in the early universe would have heated quickly as it absorbed energy. Under this model, scientists would not be able to observe any signs of the heating, which would have finished before reionization was complete.
But the slowdown caused by the presence of high-energy X-rays means that the heating should overlap the spreading transparency, allowing scientists to capture glimpses of the process.
The research was published online today (Feb. 5) in the journal Nature.
Observing the unobservable
Several radio telescopes have been constructed with the goal of observing the properties of the first stars and galaxies. The Low-Frequency Array in the Netherlands, the Precision Array for Probing the Epoch of Reionization in South Africa, and the Murchison Widefield Array in Western Australia all study the 21-centimeter (8.3 inches) wavelength, the frequency where hydrogen emission can be observed. Other telescopes are currently in the works, including the Square Kilometer Array (SKA), the 5,000-mile-wide (8,000 kilometers) grouping of telescopes spreading across South Africa and Australia.
According to experimental cosmologist Judd Bowman of Arizona State University, telescopes like the SKA should be able to detect signals emitted from the heating of the early universe, if the designers take the new research into account.
In a companion News and Views article published in the same issue of Nature, Bowman wrote, “The results should prompt astrophysicists to reconsider the wavelength range that the telescopes will target.”
Bowman, who was not part of the recent study, studies the early universe and the 21-cm line.
Though engineers designed the arrays under the assumption that reionization would be visible to the radio telescopes, the new discovery suggests that these instruments may be able to detect signs of heating by early black holes once thought to be out of reach.
Made up predominantly of gas when spotted while the Milky Way was only about 3 billion years old, the galaxy, DLA2222-0946, should one day evolve into a common spiral galaxy like the Milky Way. Yet its commonness is what makes it so important, as it should provide insights into the formation of the bulk of galaxies early in the life of the universe.
“It’s sort of extraordinary for being ordinary,” Regina Jorgenson, of the University of Hawaii, said in early January at a press conference at the American Astronomical Society meeting in Washington, D.C.
Jorgenson and her team used the Keck Telescope in Hawaii to obtain the first spatially resolved images of these young, normal galaxies. Although their existence has been known for decades, they have been a challenge to clearly resolve.
“It’s equivalent to detecting a 50-watt light bulb on Mars,” Jorgenson said.
Early galaxies contained primarily dust, the food for star formation. Jorgenson compared the process of galaxy formation to baking a cake, which requires a lot of different ingredients, the most of important of which is flour. In a galactic cake, the flour is equivalent to neutral gas, the prime fuel for star formation.
Gas doesn’t shine like stars, so astronomers had to get creative to find it in distant space. Enter a quasar, a very bright and distant astronomical source. As light from a quasar passes through these kinds of galactic systems known as DLAs, scientists can take measurements of the clouds of gas that make them up.
“These DLAs contain most of the neutral gas in the universe at the time,” Jorgenson said. “They contain most of the flour.”
But the single line of sight provided by the quasar limits how much of the galaxy can be seen. Jorgenson compared it to a single car headlight in a cloudbank. Adding to the challenge, the quasar whose bright light illuminates the galaxy also outshines it, making other emissions from the young group difficult to detect.
The team utilized used the advanced technologies of the Keck telescope to resolve the image and spectra, the measure of its separated energy wavelengths, of DLA2222-0946. Keck allowed for a significant improvement in resolution.
“It’s akin to reading the President’s newspaper in the White House [from] six miles away,” she said.
The results will be published in an upcoming edition of the Astrophysical Journal.
‘Baby Milky Ways’
Located approximately 10.8 billion light-years from the Milky Way, DLA2222-0946 formed about 3 billion years after the Big Bang (the universe is estimated to be roughly 13.8 billion years old).
When spotted, it looked nothing like the spreading spirals of the Milky Way. The young galaxy is only one-sixth the size of our galaxy and 1/200th the mass. However, the massive supply of gas contained within it means it produces about 10 times as many stars as our galaxy.
Because looking over broad distances in space is akin to looking back through time, scientists are able to see the DLA the way it appeared 10.8 billion years ago. Over time, these ‘baby Milky Way galaxies,’ as Jorgenson termed them, likely grew into galaxies that resemble our own. A clear resolution of DLA2222-0946 and other DLAs will provide insight into the evolutionary steps taken by galaxies like the Milky Way.
“This is something astronomers have been trying to do for over thirty years,” said Jorgenson.
The map shows the weather on the surface of WISE J104915.57-531906.1B (called Luhman 16B for short), the nearest brown dwarf to Earth at 6.5 light-years away. Scientists mapped the light and dark features of the failed star’s surface, according to officials with the European Southern Observatory, whose Very Large Telescope in Chile contributed to the new science. You can take video tour of the brown dwarf and its weather map on SPACE.com.
Brown dwarfs are called failed stars because they are larger than gas giant planets like Jupiter, yet still too small to produce nuclear fusion like a true star. Scientists have only found a few hundred of the odd objects, with the first confirmed 20 years ago, ESO officials said. [See more photos of strange brown dwarfs]
“Previous observations have inferred that brown dwarfs have mottled surfaces, but now we can start to directly map them,” the new study’s lead author, Ian Crossfield of the Max Planck Institute for Astronomy, said in a statement. “What we see is presumably patchy cloud cover, somewhat like we see on Jupiter.”
Crossfield and his team found that Luhman 16B probably harbors gaseous clouds made of iron and other minerals in a mostly hydrogen atmosphere. The brown dwarf rotates fully about every four hours. Weather on the brown dwarf would not be favorable for humans, however. Temperatures soar to about 2,000 degrees Fahrenheit (1,100 degrees Celsius), Max Planck officials said.
Luhman 16B is one in a pair of brown dwarfs in the southern constellation of Vela, the sail. Its brighter counterpart is known as Luhman 16A. In another study, scientists were able to dissect what is happening in different atmospheric layers on both Luhman 16B and Luhman 16A.
The two brown dwarfs were first discovered in 2013 using data from NASA’s WISE space telescope, which maps the sky in infrared light.
Scientists used Doppler imaging to create the Luhman 16B weather map, which somewhat resembles satellite weather views of Earth, Max Planck officials wrote in a news release.
“In the future, we will be able to watch cloud patterns form, evolve and dissipate — eventually, maybe exo-meteorologists will be able to predict whether a visitor to Luhman 16B can expect clear or cloudy skies,” Crossfield said in a statement.
By examining weather on brown dwarfs, scientists might be able to better understand how the atmospheres of giant planets outside of the solar system work, researchers have said.
“We’ve learned that the weather patterns on these brown dwarfs are quite complex,” Beth Biller, leader of the second study detailing the atmospheric layers, said in a statement. “The cloud structure of the brown dwarf varies quite strongly as a function of atmospheric depth and cannot be explained with a single layer of clouds.”
The brown dwarf surface-mapping results appear in the journal Nature, and the atmospheric layer results are in Astrophysical Journal Letters.
Crossfield and his team have developed a foldable oragami version of the Luhman 16B map. You can download the plans and fold your own brown dwarf here: http://www.mpia.de/Public/menu_q2e.php?Aktuelles/PR/2014/PR_2014_02/PR_2014_02_en.html
A giant gas cloud is set to spiral into the supermassive black hole at the Milky Way’s core in the next few months, and scientists should get a great view of the dramatic celestial action.
NASA’s Swift satellite will have a front-row seat for the enormous gas cloud collision, and astronomers can barely contain their excitement.
“Everyone wants to see the event happening because it’s so rare,” Nathalie Degenaar, of the University of Michigan, said in a statement.
In 2003, scientists discovered what seemed to be a cloud of gas, termed G2, which should collide in March or thereabouts with the supermassive black hole that lurks at the heart of the Milky Way. The interaction will reveal much about this black hole, which is known as Sagittarius A* (or Sag A* for short).
Although scientists have observed signs of such feeding in other galaxies, it’s rare to see these events so close to home.
With their enormous gravitational pull, the centers of black holes trap even light, making them difficult to see. But the edges of these odd objects light up up when they feed, emitting energy that can reveal details about black-hole dynamics.
Sag A* is dim even for a class of object known to be challenging to observe —almost 4,000 times fainter than astronomers expect it to be. Every 5 to 10 days, the hungry black hole gobbles down a bit of gas or dust that creates an X-ray flare that telescopes like Swift can capture.
For the last eight years, Degenaar and her team have used Swift to observe the galactic center for 17 minutes a day. On the whole, it’s been fairly quiet.
“Our supermassive black hole is laying low,” Degenaar told reporters earlier this month. “It’s not displaying a lot of action at all.”
That may well change when G2 crashes into Sag A*, since the interaction could create an X-ray flare brighter than those generated by smaller objects. Degenaar’s team, still monitoring Sag A* every day, will be in a perfect position to observe the changes, and other instruments will try to get a good look as well.
“Observatories all over the world, space- and ground-based, are ready for this,” Degenaar said.
A hidden star
While many astronomers describe G2 as a large cloud about a dozen times more massive than Earth, it could also be a smaller cloud hiding a star at its center, researchers say.
For example, the cloud could contain a variable star known as a T Tauri. But the star would likely be too faint for astronomers to detect.
“You [could] have a windy star plowing through the interstellar medium,” Leo Meyer of UCLA told reporters earlier this month.
It’s also possible that G2 contains a protoplanetary disk disrupted by tidal forces. The building of planets so close to the galactic center could inform theories of planet formation. However, such a source should have brightened more than scientists have observed.
A third option involves the product of a merged binary. At this point, astronomers aren’t sure which is the likeliest scenario.
“There is no smoking gun measurement that clearly tells us whether it is this or that,” Meyer said.
Fireworks or dud?
When G2 gets within about 200 astronomical units of Sag A*, it should start to feel strong gravitational effects. (One astronomical unit is the distance between Earth and the sun — about 93 million miles, or 150 million kilometers).
But how dramatic those effects will be is still up in the air.
“The biggest question probably is, Will there be fireworks or not?” Meyer said. “We still don’t know.”
“Fireworks” would involve the black hole brightening considerably as a significant amount of mass is dumped into it. Though he hopes for it, Meyer thinks an explosive show is unlikely.
But even if the fireworks don’t materialize, he doesn’t think the focus on the galactic center will be a loss. The resulting data should still reveal some information about the workings of Sag A*. And the last few years have produced a spike in theoretical discussions on how black holes interact with incoming material.
“Even if nothing happens, this has triggered a whole lot of thinking,” Meyer said.
On reading a new paper by Stephen Hawking that appeared online this week, you would have been forgiven in thinking the world-renowned British physicist was spoofing us. Hawking’s unpublished work — titled “Information Preservation and Weather Forecasting for Black Holes” and uploaded to the arXiv preprint service — declares that “there are no black holes.”
Keep in mind that Hawking’s bedrock theory of evaporating black holes revolutionized our understanding that the gravitational behemoths are not immortal; through a quantum quirk they leak particles (and therefore mass) via “Hawking radiation” over time. What’s more, astronomers are finding new and exciting ways to detect black holes — they are even working on an interferometer network that may, soon, be able to directly image a black hole’s event horizon!
Has Hawking changed his mind? Are black holes merely a figment of our collective imaginations? Are all those crank theories about “alternative” theories of the Cosmos true?!
Stephen Hawking hasn’t changed his mind about the whole black hole thing, but he has thrown a complex physics paradox into the limelight, one that has been gnawing at the heart of theoretical physics for the last 18 months.
Black Hole Fight Club
It all boils down to a conflict between two fundamental ideas in physics that control the very fabric of our Universe; the clash of Einstein’s general relativity and quantum dynamics. And it just so happens that the extreme environment in and around a black hole makes for the perfect “fight club” for the two theories to duke it out. But what’s the first rule of the black hole fight club? Don’t talk about the firewall, lest you get sucked into an argument with a theoretical physicist.
At a California Institute of Technology (Caltech) lecture in April 2013, Hawking and other prominent theoretical physicists had an opportunity to describe the problem at hand. Caltech’s Kip Thorne, for example, described the firewall paradox as “a burning issue in theoretical physics.”
The very basis of this burning issue is the thing that makes black holes black — the event horizon. In its most basic form, the event horizon of a black hole is the point at which even light cannot escape the gravitational clutches of the massive black hole singularity. If light cannot escape, it stands to reason that it will appear as a black sphere in space. It is a cosmic one-way street: everything goes in, nothing comes out.
An Unlucky Astronaut
In the general relativity universe, for an astronaut who had the misfortune to fall toward a black hole, he or she wouldn’t notice anything untoward as they passed across the event horizon. It would be a fairly peaceful event, no drama. “Although later on you’re doomed and you’ll encounter very strong gravitational forces that will pull you apart,” noted Caltech physicist John Preskill at the 2013 Caltech event. [The Strangest Black Holes in the Universe]
However, the quantum universe contradicts this “no drama” event horizon idea as predicted by general relativity.
In 2012, a group of physicists headed by Joseph Polchinski of the University of California in Santa Barbara revealed their finding that if black holes truly do not destroy information — a standpoint that Hawking himself reluctantly advocates — and that information can escape from the black hole through Hawking radiation, there must be a raging inferno just inside the event horizon they dub the “firewall.”
In this case, rather than falling into a “no drama” event horizon, our unlucky astronaut gets burnt to a crisp before getting ripped apart by tidal shear. This is the very antithesis of “no drama” and, therefore, a paradox.
ANALYSIS: Death By Black Hole Firewall Incineration It Shall Be
This apparent conflict between what general relativity predicts and what quantum dynamics predicts — two very established fields in physics — is precisely what theoretical physicists are trying to understand. This appears to be yet another situation where gravity and quantum dynamics don’t play nice, the solution of which may transform the way we view the Universe.
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So, when Hawking, one of the key players in the great firewall debate, writes a short paper on the topic (regardless of whether or not it has been published) the world takes note.
Hawking’s solution to the paradox removes the black hole’s event horizon, thereby removing the paradox; no event horizon, no firewall. But we’re told all black holes have event horizons — the line you cannot cross or be forever lost inside the black hole — what gives? [No Escape: How Black Holes Work (Infographic)]
Hawking thinks that the idea behind the event horizon needs to be reworked. Rather than the event horizon being a definite line beyond which even light cannot escape, Hawking invokes an “apparent horizon” that changes shape according to quantum fluctuations inside the black hole — it’s almost like a “grey area” for extreme physics. An apparent horizon wouldn’t violate either general relativity or quantum dynamics if the region just beyond the apparent horizon is a tangled, chaotic mess of information.
NEWS: Spooky Connection: Wormholes and the Quantum World
“Thus, like weather forecasting on Earth, information will effectively be lost, although there would be no loss of unitarity,” writes Hawking. This basically means that although the information can escape from the black hole, its chaotic nature ensures it cannot be interpreted, sidestepping the firewall paradox all together.
Needless to say, this paper has done little to convince Polchinski. “It almost sounds like (Hawking) is replacing the firewall with a chaos-wall, which could be the same thing,” he told New Scientist.
Much of the theoretical debate is hard to fathom and the result of calculations of physical events that we cannot possibly experience in our day to day lives. But don’t mistake this particular debate as solely a high-brow argument in the theoretical physics community. Its foundations are rooted in the growing discomfort we are feeling with the mismatch of general relativity and quantum dynamics (particularly what role gravity plays in the quantum world), a problem that cannot be solved with our current understanding of the universe.
It is, after all, these science problems that we build multi-billion dollar particle accelerators for.
In fact, the planet-forming region is so far from its star — about five times the distance between our own sun and Neptune — that it appears to be the first time researchers have seen such an arrangement for the birth of alien planets.
Japanese astronomers spotted the giant planet-forming ring while studying new images of the star named HD 142527 taken by the Atacama Large Millimeter/submillimeter Array, or ALMA, in the Chilean desert. They created a video animation of the strange planet nursery to illustrate the discovery. The star is located about 450 light-years away from Earth and is around 2 million years old. [7 Ways to Discover Alien Planets]
The powerful radio telescopes that make up ALMA offer astronomers a chance to peek at cosmic phenomena that are normally invisible. By detecting light with very short wavelengths, in the millimeter and submillimeter range, ALMA can spot the clouds of gas and dust where new stars are form, as well as the disks of debris around stare where planets are born.
The new ALMA observations of HD 142527 found that the star is surrounded by cosmic dust that could be smashing together to form planets. Especially encouraging is a bright “knot” in on the northern side of this disk — a submillimeter emission that is 30 times stronger than the southern side emission.
“We are very surprised at the brightness of the northern side,” Misato Fukagawa, an assistant professor at Osaka University, said in a statement. “I have never seen such a bright knot in such a distant position. This strong submillimeter emission can be interpreted as an indication that large amount of material is accumulated in this position. When a sufficient amount of material is accumulated, planets or comets can be formed here.”
Fukagawa and colleagues believe that if the ring has a ratio of dust to gas (1 to 100) comparable to other solar systems, then giant gas planets several times more massive than Jupiter could be forming in the disk. But if this dense knot in the ring has a higher ratio of dust, it could spawn a “dust trap” that gives rise to Earth-like rocky planets and small bodies like comets.
In any case, the solar system HD “offers a rare opportunity for us to directly observe the critical moment of planet formation and can provide new insights into the origin of wide-orbit planetary bodies,” the scientists wrote in their paper posted on the preprint service ArXiv.org.
The scientists say they hope to get more precise measurements of the amount of gas in the disk to identify what kinds of planets might be forming around the baby star. They also hope ALMA can help them spot even more planet-forming disks around other stars.
“HD 142527 is a peculiar object, as far as our limited knowledge goes,” Fukagawa added. “Our final goal is to reveal the major physical process which controls the formation of planets. To achieve this goal, it is important to obtain a comprehensive view of the planet formation through observations of many protoplanetary disks.”
The huge star MWC 656, known as a “B-emission” or “Be” star, shares space with a companion stellar-mass black hole, researchers report in a study published today (Jan. 15) in the journal Nature. Surprisingly, the black hole emits no X-ray radiation, explaining how the object had eluded detection until now.
“It is important to note that only [one other] black hole with a massive stellar companion is known in the galaxy — the bright X-ray source Cyg X-1,” study lead author Jorge Casares, of the Instituto de Astrofisica de Canarias in the Canary Islands, told SPACE.com via email. “Our discovery suggests many more black holes with massive companions may exist in the form of quiescent Be binaries.”
A strange pair
Many Be stars like MWC 656 are known to have companions — most often, small and incredibly dense supernova remnants known as neutron stars. But a black hole had never been found with a Be star until now, researchers said.
MWC 656 lies about 8,500 light-years away from Earth and is 10 to 16 times more massive than Earth’s sun. The star spins so fast, at an estimated 671,000 mph (1.08 million km/h), that huge amounts of material are ejected from its equator, creating a disk around the star.
Using two optical telescopes at the Roque de los Muchachos Observatory in the Canary Islands, Casares and his team studied emissions from this circumstellar disk. The scientists also detected optical emissions that they determined come from the “accretion disk” of gas and dust being sucked in by a nearby black hole.
Analysis of these emission lines suggests that the black hole is 3.8 to 6.9 times more massive than Earth’s sun, researchers said. It is thus a stellar-mass black hole, a type of object produced when gigantic stars run out of fuel and collapse in on themselves.
Black holes typically emit high-energy X-ray light, which is generated when the material in the black holes’ accretion disks spirals down into the hungry objects’ maws. But this isn’t happening in the MWC 656 system, likely because the companion star’s disk (which contributes to the black hole’s accretion disk) is spinning so fast.
“The absence of X-ray emission from this system is evidence that material is not channelled into the black hole. Rather, it must be retained in a holding pattern within the accretion disk,” Virginia McSwain, of Lehigh University in Pennsylvania, wrote in an accompanying commentary article in the same issue of Nature.
“Gas in the outer regions of the Be star’s disk will have high angular momentum, which will be transferred to the accretion disk during the mass transfer,” McSwain added. “Without an efficient mechanism to remove this angular momentum, accretion will be suppressed and the black hole will remain quiet.”
Back to the drawing board?
The MWC 656 system could be just the tip of the iceberg, as many more such quiescent, stellar-mass black holes may populate the universe, McSwain wrote. Astronomers may soon spot other such systems, now that they know what to look for, she added.
The new study may also force astronomers to rethink some of their ideas about the formation and evolution of black-hole systems, Casares said.
“Population synthesis models predict very few black holes survive binary evolution producing Be/black-hole binaries such as MWC 656,” he said, “the reason being that either the two stars merge before the black hole is formed or the binary gets disrupted by the supernova explosion. The fact this system is bright and relatively close indicates these binaries are more common than theory predicts, and this has strong implications for models of black hole formation and close binary evolution.”
The European Space Agency’s Gaia spacecraft lifted off its pad at Europe’s spaceport in Kourou, French Guiana at 4:12 a.m. EST (0912 GMT) Thursday, carried aloft by a Russian Soyuz-Fregat rocket. Gaia is on its way to a gravitationally stable point about 930,000 miles (1.5 million kilometers) from Earth, which it should reach in about three weeks.
Over the next five years, Gaia aims not only to pinpoint the locations of 1 billion stars in our Milky Way galaxy, but also to determine where these stars are moving, what they are made of and how luminous they are. These are all steps to help scientists better understand the history of the universe, ESA officials have said. [See photos of the Gaia spacecraft]
As a side benefit, Gaia’s powerful twin telescopes will likely find thousands of new exoplanets, asteroids and other small, faint and hard-to-see objects.
”Gaia will conduct the biggest cosmic census yet, charting the positions, motions and characteristics of a billion stars to create the most precise 3D map of our Milky Way,” ESA officials said in a statement.
A long journey
Thursday’s launch ended a long wait for the Gaia team, who saw the $1 billion (740 million euros) mission delayed from an initial 2011 launch due to telescope mirror issues, among other things.
But there is more waiting yet to come, as Gaia still has a lot of ground to cover before reaching its ultimate destination, a spot called the sun-Earth Lagrange Point 2 (L2). Lagrange points are regions in space where gravitational and orbital interactions allow spacecraft to essentially park in one spot.
And once at L2, Gaia will undergo a four-month commissioning period to make sure the spacecraft, its telescopes and other gear are working properly.
Gaia also sports a sunshield, which has two purposes: To hold solar panels to generate electricity, and to be a barrier around Gaia’s base against the heat of the sun. The spacecraft’s instruments require a temperature of minus 166 degrees Fahrenheit (minus 110 degrees Celsius) to function. With the sunshield deployed, Gaia will stretch more than 33 feet (10 meters) across.
Mapping the sky
During science operations, Gaia will spin to get a view of the entire sky. Images will be stored using a single digital camera that has almost 1 billion pixels of resolution, making it the largest digital camera ever to fly in space.
Gaia is designed to be 100 times more accurate than Hipparcos, the last high-profile ESA star-mapping mission, which flew between 1989 and 1993. Hipparcos tracked down the locations of 100,000 stars precisely, and 1 million stars with less accuracy.
Gaia’s name originally stood for Global Astrometric Interferometer for Astrophysics, but the interferometer was dropped early in the mission design because astronomers felt they could get a better view of fainter stars with an optical telescope. The name remained for project continuity.
Phosphorous — one of the essential elements for life — has been discovered in the cosmic leftovers from a star explosion for the first time, scientists say.
The finding is one of two discoveries of elements in deep space that may give scientists clues to how life is possible in the universe, researchers said. The second discovery by a second team of scientists found traces of argon gas in a distant nebula.
Life as we know it depends on a combination of many elements, principally carbon, nitrogen, oxygen, sulphur and phosphorous. While scientists have found ample abundance of the first four elements in other star explosions, new observations of the supernova remnant Cassiopeia A revealed the first evidence of phosphorus. [Amazing Photos of Supernova Explosions]
“These five elements are essential to life and can only be created in massive stars,” said Dae-Sik Moon, a University of Toronto astronomer, in a statement.
Moon is a co-author in the study that found phosphorus in Cassiopeia A. The research, led by Seoul National University astronomy Bon-Chul Koo, is detailed in the Dec. 12 edition of the journal Science along with the separate argon gas study.
“They are scattered throughout our galaxy when the star explodes, and they become part of other stars, planets and ultimately, humans,” Moon added.
Scientists estimate that the Cassiopeia A supernova remnant exploded 300 years ago. The new observations of the object were made with a spectrograph mounted on a 5-meter telescope at Palomar Observatory at the California Institute of Technology.
An eye for argon hydride
In the second study in Science today, scientists revealed the first discovery of molecules of a noble gas — a gas that is not very reactive — in space using the European Space Agency’s Herschel Space Observatory.
Astronomers were observing the Crab Nebula in infrared light when they discovered the “chemical fingerprint” of argon hydride ions. The Crab Nebula is the cosmic leftovers of a supernova explosion first described by Chinese astronomers in the year 1054.
When certain kinds of massive stars run out of fuel to burn, they explode into supernovas. The star’s destruction typically leaves behind a nebula of slowly dissipating gas as well as a star remnant, also called a neutron star.
In the Crab Nebula, the ions probably came to be due to its neutron star sending out energy that energized argon in the nebula. The argon then connected with hydrogen molecules to form the argon hydride ions, scientists said.
“Discovering argon hydride ions here was unexpected because you don’t expect an atom like argon, a noble gas, to form molecules, and you wouldn’t expect to find them in the harsh environment of a supernova remnant,” stated Mike Barlow, an astronomer at University College London in the United Kingdom who led the research.
The last stage of stellar evolution is a black dwarf. Because they emit no heat or light, these objects would be a challenge to detect if they existed today. However, at less than 14 billion years old, the universe is still too young to have created any black dwarfs!
A main sequence star that lacks the mass necessary to explode in a supernova will become a white dwarf, a ‘dead’ star that has burned through all of its hydrogen and helium fuel. But the white dwarf remains hot for some time, much like a stove burner still emits heat even when it has been turned off.
After enough time has passed, all of the leftover heat will have radiated away. No longer emitting heat or light, the white dwarf will become a black dwarf, its loss making it difficult to find. However, the black dwarf would still retain its mass, allowing scientists to detect the effects produced by its gravitational field.
But there’s no need to start searching for the elusive black dwarfs yet. At the moment, they are strictly theoretical. Scientists have calculated that a white dwarf will take tens of hundreds of billions of years to cool down and become a black dwarf. Even if a white dwarf had formed at the moment of the Big Bang — an impossibility, since a star must pass through several evolutionary stages that take at least a billion years total — it would still be a white dwarf today, having not yet sufficiently cooled.
Brown dwarfs, objects too small to have reached the point of fusion, were once called black dwarfs.
A black dwarf should not be confused with a black hole or a neutron star, both of which have been observed.