Astronomers have pieced together a detailed picture of how our Milky Way galaxy came together, using Hubble Space Telescope photos of 400 similar galaxies at various stages of evolution.
“For the first time we have direct images of what the Milky Way looked like in the past,” study co-leader Pieter van Dokkum, of Yale University in New Haven, Conn., said in a statement.
“Of course, we can’t see the Milky Way itself in the past. We selected galaxies billions of light-years away that will evolve into galaxies like the Milky Way,” van Dokkum added. “By tracing the Milky Way’s siblings, we find that our galaxy built up 90 percent of its stars between 11 billion and 7 billion years ago, which is something that has not been measured directly before.”
Hubble’s images suggest that the Milky Way started out as a faint blue object with lots of gas, clouds of which eventually collapsed to form stars. At the time of peak star formation throughout the universe — about 4 billion years after the Big Bang— galaxies like the Milky Way were pumping out about 15 new stars per year, researchers said. (For comparison, the Milky Way produces just one star a year these days.)
The data further reveal that the Milky Way’s flat disk and central bulge formed at about the same time, scientists said.
“You can see that these galaxies are fluffy and spread out,” study co-leader Shannon Patel, of Leiden University in the Netherlands, said in a statement. “There is no evidence of a bulge without a disk, around which the disk formed later.”
That’s in contrast to huge elliptical galaxies, in which the bulge appears first, team members added. Further, galaxy mergers are thought to be important in the evolution of ellipticals, while spirals like the Milky Way likely grow primarily by star formation.
“These observations show that there are at least two galaxy-formation tracks,” van Dokkum said. “Massive ellipticals form a very dense core early in the universe, including a black hole, presumably, and the rest of the galaxy slowly accretes around it, fueled by mergers with other galaxies. But from our survey we find that galaxies like our Milky Way show a different, more uniform path of growing into the majestic spirals we see today.”
The researchers incorporated data from three different Hubble Space Telescope observing programs — the 3D-HST survey, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Great Observatories Origins Deep Survey. Team members measured each of the 400 galaxies’ distance and size, which they calculated using information about its brightness and color.
Part of the team’s findings were published July 10 in The Astrophysical Journal Letters, while a second paper appears in the Nov. 11 online edition of The Astrophysical Journal.
The most distant cosmic lens — a galaxy whose gravity warps and deflects light from an even more distant stellar nursery — has been discovered by an international team of astronomers. This so-called gravitational lens, which is so distant it takes the distorted light 9.4 billion years to reach Earth, can be used to measure the mass of the faraway galaxy, according to a new study.
The discovery began as a fortuitous accident, said study lead author Arjen van der Wel, an astronomer at the Max Planck Institute for Astronomy in Germany. Researchers sifting through data collected by the Hubble Space Telescope stumbled on curious observations of a distant galaxy.
“[I] noticed a galaxy that was decidedly odd,” van der Wel said in a statement. “It looked like an extremely young galaxy, and at an even larger distance than I was aiming for. It shouldn’t even have [been] part of our observing program!” [Photos: Hubble Space Telescope's Latest Cosmic Views]
The inconsistencies suggested light was being deflected from an even more remote object that was perfectly aligned with the galaxy.
Gravity curves space and time, which means a more massive object in space will have a stronger gravitational pull. These forces bend light, warping how astronomers view cosmic objects through telescopes on Earth.
As predicted by Albert Einstein’s general theory of relativity, light that passes a distant galaxy will be affected by its gravity. As such, gravitational lenses can be useful tools. By measuring the distorted light, astronomers can determine the mass of the lensing galaxy, or the object causing the light to bend.
Furthermore, the lens naturally magnifies the background light source, which enables astronomers to observe details of galaxies that would otherwise be too distant to see.
When a gravitational lens is perfectly aligned with a distant source of light (in this case, the younger, faraway galaxy), an observer on Earth will see a circle of light. This is known as an “Einstein ring,” and it represents the projected and magnified image of the more distant object.
By comparing other images taken by the Hubble Space Telescope, and removing haze from the lensing galaxy’s collection of stars, the researchers found a near-perfect Einstein ring, according to van der Wel.
The astronomers can measure the distorted light to make direct calculations of the lensing galaxy’s mass. Yet, the discovery has also unearthed new mysteries of the early universe.
The more distant, magnified object in the study is known as a star-bursting dwarf galaxy. Typically, these types of galaxies are young, ranging from 10 million to 40 million years old, and produce new stars at a prolific rate.
A gravitational lens of this kind — in which an older galaxy deflects the light of a younger, more distant star-bursting galaxy — was thought to be extremely rare. But, this is the second star-bursting dwarf galaxy that astronomers have detected through a gravitational lens. These results suggest young, star-bursting dwarf galaxies may be more common in the early universe than was previously thought, which could force scientists to rethink some of the most commonly accepted models of galaxy evolution.
“This has been a weird and interesting discovery,” van der Wel said. “It was a completely serendipitous find, it combines two rather disparate topics I have been working on — massive, old galaxies, and young, starbursting dwarfs — and it has the potential to start a new chapter in our description of galaxy evolution in the early universe.”
The gravitational attraction of black holes is so strong that even light cannot escape their pull, making these super-dense objects invisible to outside observers and almost indistinguishable from one another.
“The accepted picture is that black holes are very simple objects that can be fully characterized by only 3 quantities: their mass, their angular momentum (how fast they spin) and their electric charge,” Thomas Sotiriou, a physicist at the International School for Advanced Studies of Trieste, told SPACE.com in an email.
The electric charge, however, is usually negligibly small, and researchers typically throw it out when describing a black hole.
Astronomer John Wheeler, who coined the term “black hole” nearly 50 years ago, famously said that “black holes have no hair” because of their simplicity. Now “hair” is used as a colloquial term among physicists as a stand-in for any other measure needed to describe a black hole that departs from the traditional three-quantity model.
For their study, Sotiriou and his colleagues looked at black holes in the context of the equations of scalar-tensor theories of gravity.
“These are theories different than Einstein’s theory, general relativity,” Sotiriou wrote in an email. “They also describe the gravitational field in term of curvature of spacetime and predict the existence of black holes. However, they include also a different kind of field — a scalar field — to participate to the mediation of the gravitational interaction.”
The researchers found that black holes develop scalar “hair” when ordinary matter surrounds them.
“This does not happen in the standard picture,” Sotiriou said.
It’s not clear from the study if these strands of scalar “hair” make black holes look much different from the standard picture, and it’s not clear how observable the effect is with current technology, Sotiriou explained.
Not only would the existence of “hair” help researchers understand the structure of black holes themselves, proof of “hairy” black holes could represent a paradigm shift, Sotiriou said, since Einstein’s theory does not include a scalar field.
The dwarf planet Ceres, which orbits the sun in the asteroid belt between Mars and Jupiter, is a unique body in the solar system, bearing many similarities to Jupiter’s moon Europaand Saturn’s moon Enceladus, both considered to be potential sources for harboring life.
“I think of Ceres actually as a game changer in the solar system,” Schmidt said.
“Ceres is arguably the only one of its kind.”
The innermost icy body
When Ceres was discovered in 1801, astronomers first classified it as a planet. The massive body traveled between Mars and Jupiter, where scientists had mathematically predicted a planet should lie. Further observations revealed that a number of small bodies littered the region, and Ceres was downgraded to just another asteroid within the asteroid belt. It wasn’t until Pluto was classified as a dwarf planetin 2006 that Ceres was upgraded to the same level.
Ceres is the most massive body in the asteroid belt, and larger than some of the icy moons scientists consider ideal for hosting life. It is twice the size of Enceladus, Saturn’s geyser-spouting moon that may hide liquid water beneath its surface.
Unlike other asteroids, the Texas-sized Cereshas a perfectly rounded shape that hints toward its origins.
“The fact that Ceres is so round tells us that it almost certainly had to form in the early solar system,” Schmidt said. She explained that a later formation would have created a less rounded shape.
The shape of the dwarf planet, combined with its size and total mass, reveal a body of incredibly low density.
“Underneath this dusty, dirty, clay-type surface, we think that Ceres might be icy,” Schmidt said. “It could potentially have had an ocean at one point in its history.”
“The difference between Ceres and other icy bodies [in the solar system] is that it’s the closest to the sun,” Castillo-Rogez said.
Less than three times as far as Earth from the sun, Ceres is close enough to feel the warmth of the star, allowing ice to melt and reform.
Investigating the interior of the dwarf planet could provide insight into the early solar system, especially locations where water and other volatiles might have existed.
“Ceres is like the gatekeeper to the history of water in the middle solar system,” Schmidt said.
Studying the surface
As large as Ceres is, its distance has made it a challenge to study from Earth. Images taken by the space-based Hubble Space Telescope provided some insight to its surface, but to be sighted, features could be no larger than 25 kilometers (15.5 miles) in diameter.
Several round circular spots mar the terrain, features which Schmidt said could be any one of a number of geologic terrains, including potentially impact basins or chaos terrains similar to those found on Europa. The largest of these, named Piazzi in honor of the dwarf planet’s discoverer, has a diameter of about 250 km (155 miles). If this feature is an impact basin, it would have been formed by an object approximately 25 km (15.5 miles) in size.
But for Schmidt, this is another possible indication about the dwarf planet’s surface.
“It doesn’t mean that Ceres hasn’t been hit by something bigger than 25 kilometers,” she said. “It just means that whatever is going on on Ceres has totally erased [the topographic signature of that event].”
Ceres may have suffered major impacts, especially during periods of heavy bombardment early in the solar system’s history. If the surface contained ice, however, those features may have been erased.
Telescopes on Earth have also been able to study the light reflecting from the planet and read its spectra.
“The spectrum is telling you that water has been involved in the creation of materials on the surface,” Schmidt said.
The spectrum indicates that water is bound up in the material on the surface of Ceres, forming a clay. Schmidt compared it to the recent talk of mineralsfound by NASA’s Curiosityon the surface of Mars. [The Search for Life on Mars (A Photo Timeline)]
“[Water is] literally bathing the surface of Ceres,” she said.
In addition, astronomers have found evidence of carbonates, minerals that form in a process involving water and heat. Carbonates are often produced by living processes.
The original material formed with Ceres has mixed with impacting material over the last 4.5 billion years, creating what Schmidt calls “this mixture of water-rich materials that we find on habitable planets like the Earth and potentially habitable planets like Mars.”
A prime site for life?
Water is considered a necessary ingredient for the evolution of life as we know it. Planets that may have once contained water, such as Mars, as well as moons that could contain it today, like Enceladus and Europa, are all thought to be ideal for hosting or having once hosted life.
Because of its size and closeness, Schmidt calls Ceres “arguably more interesting than some of these icy satellites.”
“If it’s icy, it had to have an ocean at some point in time,” she said.
Castillo-Rogez compared Earth, Europa, and Ceres, and found that the dwarf planet bore many similarities to Earth, perhaps more than Jupiter’s icy moon. Both Earth and Ceres use the Sun as a key heat source, while Europa takes its heat from its tidal interaction with Jupiter. In addition, the surface temperature of the dwarf planet averages 130 to 200 degrees Kelvin, compared to Earth’s 300 K, while Europa is a frosty 50 to 110 K.
“At least at the equator where the surface is warmer, Ceres could have preserved a liquid of sorts,” Castillo-Rogez said.
Liquid water could exist at other points on the dwarf planet known as cold traps, shadowed areas where frozen water could remain on the surface. Such icy puddles have been found on Earth’s moon. [Photos: Europa, Mysterious, Icy Moon of Jupiter]
“The chemistry, thermal activity, the heat source, and the prospect for convection within the ice shell are the key ones that make us think that Ceres could have been habitableat least at some point in its history,” Castillo-Rogez said.
The future of Ceres
As scientists develop more information about Europa and Enceladus, there has been a greater call to investigate the two prime sites for life. But Schmidt and Castillo-Rogez think that Ceres could also be a great boon for astrobiology and space exploration.
“It’s not a difficult environment to investigate,” she said. “As we think about the future of landed missions for people and rovers, why not go to Ceres?”
Though it would be more challenging to drill into than Europa, which boasts an icy surface layer, the dwarf planet would make a great site to rove around on. Schmidt also noted that it could make a great launching point when it comes to reaching the outer solar system. Its smaller mass would make it easier to land on — and leave — than Mars, which could make it a good site for manned missions.
“We have such a big planet bias, we have such a bias for things that look exactly like us,” Schmidt said.
“In this kind of special place in the solar system, we have a very unique object that might be telling us a lot about what we don’t know about building a habitable planet.”
NASA’s Dawn mission launched September 27, 2007. It traveled to the asteroid Vesta, where it remained in orbit from July 2011 to July 2012 before heading to Ceres. It is slated to spend five months studying the dwarf planet, though Schmidt expressed hope that the craft would continue working beyond the nominal mission, allowing the team to study the icy body even longer.
Castillo-Rogez pointed out that not only will Dawn reach Ceres in 2015, the European Space Agency’s Rosetta spacecraft will be escorting the comet Churyumov-Gerasimenko around the sun that year, while NASA’s New Horizons mission will be reaching Pluto and its moon Charon.
“’15 is going to be a great year for icy bodies,” Castillo-Rogez said.
“I think when we get to Ceres, it’s just going to be an absolute game changer, a new window into the solar system that we wouldn’t have without going there,” Schmidt said.
The best look yet at mysterious brown dwarfs, strange cosmic oddities that blur the lines between stars and planets, has revealed just how large and cold they really are, scientists say. In fact, the weird “failed stars” only get as hot as your kitchen oven.
The new discovery may shed light on the formation and evolution of distant alien worlds, researchers added.
Starlike bodies known as brown dwarfs are often billed as failed stars because they are larger than planets, but too small to trigger nuclear fusion and ignite into the brilliance of a full-fledged star.
As such, brown dwarfs have only what little heat they are born with. [Top 10 Star Mysteries]
These new findings suggest the coldest brown dwarfs are between about 260 and 350 degrees Fahrenheit (125 and 175 degrees Celsius), with masses five to 20 times greater than the size of Jupiter. The temperature of the sun, for example, is about 10,000 F (5,500 C) at its surface.
“These objects we were studying were suspected to be colder than anything else that had previously been discovered in the solar neighborhood,” said study lead author Trent Dupuy, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Several hundred have been detected to date.
Chilly brown dwarf science
Scientists discovered the coldest type of brown dwarfs two years ago, which theoretical models suggested could at times be even cooler than the human body.
“Astronomers are always looking for colder and colder free-floating, starlike objects,” Dupuy told SPACE.com. “One key reason for this is that their atmospheres have similar temperatures to many of the gas giant planets that have been discovered orbiting stars other than the sun. So they are like little laboratories where you can study atmospheric physics relevant to extrasolar planets, but without the glare of their host star.”
However, the dim and distant nature of these cold brown dwarfs made it difficult to confirm just how far away, large, bright and cold they actually were.
“Because they were not like anything that had been seen before, we couldn’t really be sure what we were dealing with,” Dupuy said.
Now, using NASA’s Spitzer Space Telescope, astronomers have measured the precise distances to eight cold brown dwarfs. This, in turn, helped them calculate just how bright, cold and massive they are.
The researchers analyzed how the distance of these brown dwarfs appeared to vary in relation to more distant background stars as the Earth completed an orbit around the sun. This helped triangulate the position of these brown dwarfs. These changes are very subtle, requiring the scientists to patiently gather data for a year.
Once the astronomers knew how far away these brown dwarfs were, they could deduce how bright and cool they must be for their light and heat to be detected. Based on this data, the researchers could then model how massive they were.
The colossal black hole at the heart of the Milky Way galaxy is a messy eater. Of all the gas that falls toward the black hole, 99 percent gets spewed back out into space, new observations show, making the black hole akin to a toddler whose food ends up mostly on the floor, rather than his mouth.
The Milky Way’s super-massive black hole, called Sagittarius A* (pronounced “Sagittarius A-star”), contains the mass of 4 million suns. Yet it’s not getting much larger, according to the new findings, which help explain why the object is surprisingly dim.
Although black holes themselves can’t be seen, their immediate vicinities usually emit strong radiation from the material falling into them. Not so for Sgr A*, though, which has prompted a rash of competing theories trying to explain its surprising lack of light. [Strangest Black Holes In the Universe]
“There’s been a debate for the last 20 years or so about what actually is happening to the matter around the black hole,” said research leader Q. Daniel Wang of the University of Massachusetts, Amherst. “Whether the black hole is accreting the matter, or actually whether the matter can be ejected. This is the first direct evidence for outlflow in the accretion process.”
The new findings show definitively that most of the matter in the gas cloud surrounding the black hole is ejected out into space, which explains why it doesn’t release light on its way in to be eaten.
3 million seconds
The discovery comes via new observations taken by NASA’s Chandra X-Ray Observatory that required the equivalent of about five weeks of observing time (Wang gave the amount of time as 3 megaseconds, or 3 million seconds), spread out over months, to achieve unparalleled resolution of the area around Sagittarius A*.
The X-ray views focused on the cloud of hot gas surrounding the black hole, and found that there was much less higher-temperature gas than lower-temperature gas there. Because mass heats up as it falls toward a black hole, the researchers were able to infer that gas was being lost during this process. “There must be ejection of matter when the gas is moving in,” Wang explained.
“Exactly how it happens is not totally clear,” Wang told SPACE.com. “There are all kinds of simulations and theories which predict that it should occur. But this is the first observational evidence that can say this does occur.”
Scientists still have a ways to go to see the area in enough detail to decipher the mechanism for the gas ejection, he said. They also don’t yet know where all this gas goes, he added.
Ruled out theories
The new observations definitively rule out some theories that had attempted to explain the perplexing dimness of Sgr A*, such as one idea that most of the light there was being emitted by a potential group of rapidly rotating low-mass stars.
Wang and his colleagues’ findings are detailed in the Aug. 30 issue of the journal Science.
“This result is important not only for Sgr A*, but also all other
low-luminosity black holes, since we now have a better understanding of
their radiative efficiency, i.e., how to relate the light that we see to
the amount of gas actually getting accreted onto the black hole,” astrophysicist Jeremy Schnittman of NASA’s Goddard Space Flight Center in Greenbelt, Md., wrote in an email. Schnittman was not involved in the research, but wrote a commentary article on the findings published in the same issue of Science.
The new data also offer some evidence for where the gas cloud comes from. The Chandra observations show its shape in better detail than ever before, and suggest that it closely mirrors the distribution of a group of massive stars previously seen there, which have formed a disc. Massive stars are known to emit strong winds of material that fly out at superfast speeds. Wind from these stars is likely colliding, producing the hot plasma of gas found around the black hole, Wang said.
Many of the researchers ideas about Sagittarius A* can be further tested in the coming months when a rare event occurs. A small cloud of gas is on a collision course with the black hole, and is due to be gobbled up before scientists’ eyes. Because this cloud is made of cold and not hot gas, it’s expected to be almost fully consumed by Sagittarius A*.
“It will be really interesting to see what happens when the G2 cloud approaches later this year,” Schnittman told SPACE.com in an email. “Will the efficiency change when the accretion rate goes up? Is there an abrupt transition to a new type of accretion? Will we see anything different at all?”
The ALMA radio telescope, a joint project between North America, Europe and Asia, recorded the star birth images. They show the nascent star unleashing material at hundreds of kilometers per second, which then slams into carbon monoxide molecules, causing them to glow. The glowing object spawned by the newborn star is what scientists call a Herbig-Haro object. European Southern Observatory officials used the new views to create a video tour of new star birth images.
“This system is similar to most isolated low mass stars during their formation and birth,” Diego Mardones, a co-author of the study detailing the stellar findings said in a statement. “But it is also unusual because the outflow impacts the cloud directly on one side of the young star and escapes out of the cloud on the other. This makes it an excellent system for studying the impact of the stellar winds on the parent cloud from which the young star is formed.” [See ALMA's photos of the baby star and Herbig-Haro object]
The new image of Herbig-Haro 46/47 (HH 46/47) produced by the ALMA telescope, its name is short for Atacama Large Millimeter/submillimeter Array, reveals two jets of material streaming away from the newborn star, one of which was never detected before.
One jet appears on the left side of the photo in pink and purple streaming partially toward Earth, while the orange and green jet on the right-hand-side show a jet pointed away from Earth.
ALMA’s sensitive instrumentation took five hours to get these results. Earlier photos taken with other telescopes did not catch the second (orange and green) jet stream because dust surrounding the star obscured their views.
Astronomers observing the object with ALMA were also able to measure how quickly the glowing material is speeding through the cosmos, ESO officials said. The ejecta is moving at a much higher clip than previously measured, meaning that the outflowing gas has more energy and momentum than expected.
“ALMA’s exquisite sensitivity allows the detection of previously unseen features in this source, like this very fast outflow,” Héctor Arce, the lead author of the study appearing in the Astrophysical Journal, said in a statement. “It also seems to be a textbook example of a simple model where the molecular outflow is generated by a wide-angle wind from the young star.”
The $1.3 billion ALMA radio telescope is an array of 66 of individual radio telescopes that create one of the most powerful telescopes ever built. Each dish is up to 40 feet wide (12 meters) and can weigh 115 tons. The combined effort of the telescopes allows scientists to see celestial sights invisible in optical light because they are masked by gas and dust.
New observations from NASA’s Hubble Space Telescope have helped astronomers crack a longstanding puzzle about galaxy evolution.
For years, scientists have wondered why galaxies that have ceased forming new stars — so-called “quenched galaxies” — were smaller long ago than they are today. Perhaps, they thought, ancient quenched galaxies continued to grow by merging with smaller cousins that had also stopped producing stars.
But that hypothesis is off the mark, a new study reports.
“We found that a large number of the bigger galaxies instead switch off at later times, joining their smaller quenched siblings and giving the mistaken impression of individual galaxy growth over time,”co-author Simon Lilly, of the Swiss Federal Institute of Technology in Zurich, said in a statement.
The researchers used observations from Hubble’s Cosmic Evolution Survey (COSMOS), the Canada-France-Hawaii Telescope and the Subaru Telescope to map an area of the sky about nine times the size of the full moon. They used the observations to make a video of the quenched galaxies as seen by Hubble.
The team studied and tracked the quenched galaxies in this patch through the last eight billion years of the universe’s history, eventually determining that most of them did not grow over time but rather remained small and compact.
So it appears that star production simply switched off earlier in older galaxies compared to younger ones. This makes sense, researchers said; star-forming galaxies were smaller in the early universe, after all, so they would hit growth and evolution milestones at a relatively smaller size.
“The apparent puffing up of quenched galaxies has been one of the biggest puzzles about galaxy evolution for many years,”said lead author Marcella Carollo, also of the Swiss Federal Institute of Technology in Zurich. “Our study offers a surprisingly simple and obvious explanation to this puzzle. Whenever we see simplicity in nature a midst apparent complexity, it’s very satisfying.”
The Hubble Space Telescope, a collaboration between NASA and the European Space Agency, has made more than 1 million science observations since its launch in 1990, and it’s still going strong. NASA announced earlier this year that it had extended the telescope’s science operations through April 2016.
A newly discovered way to determine the spin of monster black holes could help shed light on the evolution of these bizarre objects and the galaxies they anchor.
Astronomers watched as a black hole that sits at the core of a spiral galaxy 500 million light-years from Earth gobbled up gas and dust from its surrounding accretion disk. They were able to measure the distance between the inner edge of the disk and the black hole, which, in turn, allowed them to estimate the black hole’s spin.
“If a black hole is spinning, it drags space and time with it, and that drags the accretion disk, containing the black hole’s food, closer towards it,” study lead author Chris Done, of the University of Durham in the United Kingdom, said in a statement. “This makes the black hole spin faster — a bit like an ice skater doing a pirouette.” [Gallery: Black Holes of the Universe]
Researchers said the technique could help astronomers address broad questions about galactic evolution, which is intimately tied to the growth and activity of the supermassive black holes that lurk at the heart of most, if not all, galaxies.
“Understanding this connection between stars in a galaxy and the growth of a black hole, and vice versa, is the key to understanding how galaxies form throughout cosmic time,” Done said.
Done and her colleagues used the European Space Agency’s XMM-Newton satellite to study the distant supermassive black hole, which contains as much mass as 10 million suns.
This black hole blasts out prodigious amounts of energy as it feeds on the material in its accretion disk. XMM-Newton observed this output in optical, ultraviolet and X-ray wavelengths, enabling the astronomers to measure how far the disk sits from the black hole.
Astronomers have calculated the spin of supermassive black holes before. In February, for example, a different research team determined the rotation rate of the black hole at the center of a spiral galaxy called NGC 1365. That group inferred the spin speed by measuring the distortion of high-energy light emitted by iron atoms in the accretion disk.
It’s tough to describe black-hole spin rates because they don’t really translate into familiar terms, such as miles per hour. For example, the NGC 1365 team, which used observations by XMM-Newton and NASA’s NuStar spacecraft, found the black hole’s rotation rate to be 84 percent of the maximum allowed by Einstein’s theory of general relativity.
In the new study, Done and her team estimated that the black hole found 500 million light-years away — which is powering a superluminous “active galactic nucleus” known as PG1244+026 — has a relatively low spin rate.
“This contrasts with the recent X-ray determinations of (close to) maximal black hole spin in other [similar galaxies] based on relativistic smearing of the iron profile,” the researchers wrote in the study, which was published online today (July 29) in the journal Monthly Notices of the Royal Astronomical Society.
“Better high-energy data are required in order to determine whether this new method gives a spin estimate which is consistent with that derived from the iron line, or whether it instead reveals a lack of understanding of disc continuum emission and/or of disc reflection,” the team wrote.
Their observations suggest that the space cloud will be completely ripped apart over the next year as it swirls closer to the galactic drain.
Most galaxies are thought to have enormous black holes at their center, and the one at the middle of the Milky Way — roughly 25,000 light years from Earth — has a mass about four million times that of the sun. [Milky Way's Black Hole Rips Apart Gas Cloud (Video)]
Scientists first spotted a gas cloud accelerating toward our galaxy’s supermassive black hole in 2011. Data from 2004 show that the cloud was once shaped like a circular blob, but the intense gravitational forces of the black hole have now stretched it spaghetti-thin, researchers say.
Their new observations were made this past April with the European Southern Observatory’s Very Large Telescope (VLT) in Chile. The cloud’s light becomes more difficult to spot the more it gets stretched, but a 20-hour exposure with the VLT’s special infrared spectrometer, called SINFONI, allowed scientists to measure the cosmic body getting closer to its doom.
Scientists still don’t know where exactly the gas cloud came from, but they say the new observations rule out some possibilities.
“Like an unfortunate astronaut in a science fiction film, we see that the cloud is now being stretched so much that it resembles spaghetti,” Stefan Gillessen, of the Max Planck Institute for Extraterrestrial Physics in Germany, who led the observing team, said in a statement. “This means that it probably doesn’t have a star in it. At the moment we think that the gas probably came from the stars we see orbiting the black hole.”
At its closest approach, the grossly stretched cloud is a little more than 15 billion miles (25 billion km) from the black hole itself — about five times Neptune’s distance from the sun, the researchers say. This is dangerously close considering the black hole’s humongous mass, and the cloud, Gillessen says, is “barely escaping falling right in.”
Gillessen and colleagues say the head of the cloud has already whipped around the black hole and is speeding back in our direction at more than 6.2 million mph (10 million km/h), roughly one percent the speed of light. The tail is following at a slower pace (about 1.6 million mph, or 2.6 million km/h).
“The cloud is so stretched that the close approach is not a single event but rather a process that extends over a period of at least one year,” Gillessen said in a statement.
The new observations will be detailed in the Astrophysical Journal. Scientists plan to intensely monitor the region throughout the year to watch as the cloud gets completely torn apart — a rare opportunity to test theories about how black holes pull in mass.
Physics cannot describe what happens inside a black hole. There, current theories break down, and general relativity collides with quantum mechanics, creating what’s called a singularity, or a point at which the equations spit out infinities.
But some advanced physics theories are trying to bridge the gap between general relativity and quantum mechanics, to understand what’s truly going on inside the densest objects in the universe. Recently, scientists applied a theory called loop quantum gravity to the case of black holes, and found that inside these objects, space and time may be extremely curved, but that gravity there is not infinite, as general relativity predicts.
This was the first time scientists have applied the full loop quantum gravity theory to black holes, and the results were encouraging, researchers said.
“What they have done is a major step, because they have been able to provide a much more complete description of what really happens near the black hole singularity using loop quantum gravity,” said Abhay Ashtekar, a physicist who studies loop quantum gravity at Pennsylvania State University, who was not involved in the new research.”We still don’t have a clear picture of the details of what happens. So it is opening a new door that other people will follow.” [Images: Black Holes of the Universe]
A black hole is created when a huge star runs out of fuel for nuclear fusion and collapses under its own gravity. The star’s outer layers are expelled, and its core falls in on itself, with the pull of gravity becoming ever stronger, until what’s left is the core’s mass condensed into an extremely small area. According to general relativity, this area is a single point of space-time, and the density there is infinitely large — a singularity.
But most scientists think singularities don’t really exist, that they’re just a sign that equations have broken down and fail to adequately describe reality. Loop quantum gravity appears to be an improvement on general relativity in describing black holes because it doesn’t produce a singularity.
The idea is based on the notion of “quantization,” which breaks an entity up into discrete pieces.Whilequantum mechanics says atoms exist in quantized, discrete states, loop quantum gravity posits that space-time itself is made of quantized, discrete bits, in the form of tiny, one-dimensional loops.
“The loop means the fundamental excitations of space-time themselves are one-dimensional in nature,” said Jorge Pullin, a physicist at Louisiana State University, who co-authored the new study with Rodolfo Gambini of the University of the Republic in Montevideo, Uruguay. “The fundamental building block is a loop, or network of loops. For a visual image, think of a mesh fabric.”
This way of portraying space-time changes fundamental physics, especially in extreme settingssuch as black holes or the Big Bang — which is thought to have birthed the universe. The Big Bang, like black holes, is indescribable under general relativity, understood only as a singularity.
“The subject really took off in 2005 when it was realized loop quantum gravity can naturally resolve the Big Bang singularity and that quantum space-time is much larger than what Einstein envisioned,” Ashtekar told SPACE.com.
Pullin and Gambini said their work is just a preliminary step, far from a full description of the true complexity of black holes.
“This model we’ve done is extremely simple,” Pullin said. Under their simplified model,”the black hole exists forever and doesn’t evolve. As a consequence I cannot tell you exactly what nature is going to do inside a black hole. It could be that the singularity gets replaced by a region that gets highly curved, but not infinitely curved. Or it could be that it just doesn’t make sense — you get a region which doesn’t behave like classical space-time. It would interact with particles in different ways than we normally think.”
Now that they’ve achieved this step, the researchers hope to advance their work by making the black holes in their model more dynamic and changeable.
“The black holes we studied were in empty space — there was no matter in them. They were pure space-time,” Pullin said.”We’re trying to add matter, because then it adds dynamics. We’re in the middle of that now.”
Black holes are essentially invisible, but astronomers are developing technology to image the immediate surroundings of these enigmas like never before. Within a few years, experts say, scientists may have the first-ever picture of the environment around a black hole, and could even spot the theorized “shadow” of a black hole itself.
Black holes are hard to see in detail because the large ones are all far away. The closest supermassive black hole is the one thought to inhabit the center of the Milky Way, called Sagittarius A* (pronounced “Sagittarius A-star”), which lies about 26,000 light-years away. This is the first target for an ambitious international project to image a black hole in greater detail than ever before, called the Event Horizon Telescope (EHT).
The EHT will combine observations from telescopes all over the world, including facilities in the United States, Mexico, Chile, France, Greenland and the South Pole, into one virtual image with a resolution equal to what would be achieved by a single telescope the size of the distance between the separated facilities.
“This is really an unprecedented, unique experiment,” said EHT team member Jason Dexter, an astrophysical theorist at the University of California, Berkeley. “It’s going to give us more direct information than we’ve ever had to understand what happens extremely close to black holes. It’s very exciting, and this project is really going to come of age and start delivering amazing results in the next few years.”
From Earth, Sagittarius A* looks about as big as a grapefruit would on the moon. When the Event Horizon Telescope is fully realized, it should be able to resolve details about the size of a golf ball on the moon. That’s close enough to see the light emitted by gas as it spirals in toward its doom inside the black hole.
Very long baseline interferometry
To accomplish such fine resolution, the project takes advantage of a technique called very long baseline interferometry (VLBI). In VLBI, a supercomputer acts as a giant telescope lens, in effect.
“If you have telescopes around the world you can make a virtual Earth-sized telescope,” said Shep Doeleman, an astronomer at MIT’s Haystack Observatory in Massachusetts who’s leading the Event Horizon Telescope project. “In a typical telescope, light bounces off a precisely curved surface and all the light gets focused into a focal plane. The way VLBI works is, we have to freeze the light, capture it, record it perfectly faithfully on the recording system, then shift the data back to a central supercomputer, which compares the light from California and Hawaii and the other locations, and synthesizes it. The lens becomes a supercomputer here at MIT.”
A major improvement to the Event Horizon Telescope’s imaging ability will come when the 64 radio dishes of the ALMA (Atacama Large Millimeter/submillimeter Array) observatory in Chile join the project in the next few years.
“It’s going to increase the sensitivity of the Event Horizon Telescope by a factor of 10,” Doeleman said. “Whenever you change something by an order of magnitude, wonderful things happen.” [Photos: ALMA Inaugurated in Chile]
Very long baseline interferometry has been used for about 50 years, but never before at such a high frequency, or short wavelength, of light. This short-wavelength light is what’s needed to achieve the angular resolution required to measure and image black holes.
Grand technical challenge
Pulling off the Event Horizon Telescope has been a grand technical challenge on many fronts.
To coordinate the observations of so many telescopes spread out around the world, scientists have needed to harness specialized computing algorithms, not to mention powerful supercomputers. Plus, to accommodate the time difference between the various stations, extremely accurate clocks are needed.
“We had to prove you could keep time well enough at all the stations, and that the detectors at all the telescopes were good enough, that when you multiply the two signals from two telescopes you wouldn’t get just noise,” said Dan Marrone, an astronomer at the University of Arizona’s Steward Observatory who’s building a receiver to enable the South Pole Telescope to join the project. [No Escape: Dive Into a Black Hole (Infographic)]
The researchers have been using atomic clocks made of what’s called hydrogen masers to keep time to an accuracy of about a trillionth of a second per second.
“We use this property of the structure of the hydrogen atom to create a fundamental time reference for us that transitions between two states of the electron in a hydrogen atom,” Marrone said. “It creates a low-frequency signal that through careful design you can make a very precise oscillator. It creates very perfect oscillations for a short time period. That means we can average our data over those time periods because they will all have kept time very perfectly.”
Testing general relativity
With the unprecedented data soon to be collected by the Event Horizon Telescope, scientists are hoping to better understand the strange physics of black holes, which are some of the most extreme, bizarre objects in the universe.
The black hole at the center of the Milky Way is thought to contain the mass of about 4 million suns, all packed into an incomprehensibly small area. The ultra-strong densities there should produce some very extreme gravitational forces that offer a rare test of Einstein’s general theory of relativity.
“The Event Horizon Telescope is going to look at emission at the edge of the black hole itself,” Doeleman said. “That’s an area where the gravity is so strong that light is bent and the structures you see are dominated by strong gravity, where you absolutely need Einstein to understand what you’re seeing. It becomes a laboratory of extremes.”
One question scientists hope to answer is whether black holes really have event horizons, as predicted by general relativity. An event horizon is a theorized boundary around a black hole that marks the “point of no return” where matter and even light can’t escape. If event horizons exist, general relativity also predicts black holes will have shadows, or darkened regions where light has been swallowed. If black holes do produce shadows, the Event Horizon Telescope should be able to see one at Sagittarius A* within the next few years, said Dexter, the University of California, Berkeley, theorist.
“That would be the most extreme general relativistic effect detected so far,” he added.
X-raying black holes
While the Event Horizon Telescope is observing black holes in radio wavelengths, the other frontier of black hole astronomy is in the X-ray regime.
The gas falling into black holes emits light across the electromagnetic spectrum, but the hottest, most energetic gas, which is swirling closest to a black hole’s event horizon, can be seen in X-ray light.
This light is only visible beyond the atmosphere of Earth, to space telescopes such as NASA’s Chandra observatory and NuSTAR telescope, Europe’s XMM Newton observatory, and Japan’s Suzaku telescope. These observations aren’t directly imaging the environs of black holes, like the Event Horizon Telescope, but are breaking up X-ray light into its constituent colors, or wavelengths, to search for clues about what’s happening to the gas in those extreme environments.
For example, astronomer Chris Reynolds of the University of Maryland, College Park, uses X-ray observations to study the spins of black holes. “Because the physics is so extreme, when a black hole spins, it actually twists up the space-time around it and we can see the effect it has on gas orbiting the black hole,” Reynolds said.
And by studying black holes in various wavelengths, researchers hope to build up a more complete understanding of these strange cosmic objects.
“The gas, as it falls into a black hole, emits radio waves, which is what the Event Horizon Telescope is trying to see, and it also makes X-rays, and that gives you very complementary views on the properties of the infalling gas and the black hole,” Reynolds said. “The Event Horizon Telescope is on the threshold of some extremely close results, and we’re all looking forward to it.”
The most detailed observations to date of the material surrounding a gigantic black hole have surprised scientists, who say what they see conflicts with common theories about these powerful objects.
Astronomers used the European Southern Observatory’s Very Large Telescope Interferometer in Chile to observe the dust around the supermassive black hole at the center of the NGC 3783 galaxy, which lies tens of millions of light-years awayin the constellation Centaurus. The black hole, like many at the centers of galaxies, is gorging on a feast of mass that’s fallen toward it from the surrounding area. As the dust falls in, it releases powerful radiation that can be spotted from across the universe.
When observing NGC 3783′s center, the researchers expected to find almost all of the dust in the shape of a doughnut orbiting the black hole, but instead found significant amounts of material above and below the doughnut, or torus, shape. [Images: How Magnetic Fields Shape Black Holes]
The dust inside the doughnut is hot, reaching temperatures of 1,300 to 1,800 degrees Fahrenheit (700 to 1,000 degrees Celsius), but the dust that’s been blown away has cooled down, the astronomers reported. A paper detailing the findings was published today (June 20) in the Astrophysical Journal by lead author Sebastian Hönig of the University of California, Santa Barbara and Christian-Albrechts-Universität zu Kiel in Germany, and his colleagues.
These observations suggest that the intense radiation produced when black holes feed on surrounding material also pushes some of this material outward. The discovery could lead to a “paradigm shift” in the understanding of how active supermassive black holes like this operate, scientists with the European Southern Observatory wrote in a statement.
“This is the first time we’ve been able to combine detailed mid-infrared observations of the cool, room-temperature dust around an AGN with similarly detailed observations of the very hot dust,” Hönig said in a statement.
Astronomers hope to use this new knowledge to piece together a fuller picture of how black holes evolve within galaxies.
A new instrument being developed for the Very Large Telescope Interferometer called Matisse should help scientists gather even more detailed observations of supermassive black holes. The Very Large Telescope Interferometer combines light from four separate telescopes to create extremely detailed amalgam observations.
“I am now really looking forward to Matisse, which will allow us to combine all four VLT Unit Telescopes at once and observe simultaneously in the near- and mid-infrared — giving us much more detailed data,” Hönig said.
A nebula that shines about 5,500 light-years from Earth could be going through a “baby boom,” according to a new study.
NGC 6334 (the Cat’s Paw Nebula) might be one of the most productive star-forming regions in the Milky Way. The nebula is home to tens of thousands of newly formed stars and plays host to about 200,000 suns’ worth of star-creating material.
“NGC 6334 is forming stars at a more rapid pace than Orion — so rapidly that it appears to be undergoing what might be called a burst of star formation,” the study’s lead author Sarah Willis of the Harvard-Smithsonian Center for Astrophysics (CfA) and Iowa State University said in a statement. “It might resemble a ‘mini-starburst,’ similar to a scaled-down version of the spectacular bursts sometimes seen in other galaxies.”
More than 2,000 of the stars in the nebula are very young and are still trapped inside the “dusty cocoons” that birthed them, scientists said. Willis presented the new findings here today (June 5) at the 222nd meeting of the American Astronomical Society.
Astronomers have observed distant, bright starbursting galaxies before, but because the Cat’s Paw Nebula is a region within the Milky Way, scientists can get a better sense of why starburst regions might form and what they look like closer-up.
“Because NGC 6334 is nearby, astronomers can probe it in much greater detail, even down to counting the numbers of individual stars of various types and ages,” CfA officials wrote.
Astronomers are still trying to investigate the origin of the starburst. Some researchers think that a blast from a supernova explosion or galactic collisions could create starbursts; however, neither of those explanations appear to explain the Cat’s Paw Nebula’s recent activity.
Scientists expect that the starburst will last for a relatively short amount of time in cosmic terms. In total, NGC 6334′s burst will probably endure for only a few million years.
“We’re lucky, not only because it’s nearby but also because we’re catching it while the starburst is happening,” Willis said.
There’s a chance that NASA’s Kepler space telescope can recover from the malfunction that has halted its wildly successful search for alien planets, mission team members say.
The second of Kepler’s four reaction wheels — devices that allow the observatory to maintain its position in space — has failed, depriving Kepler of the ability to lock precisely onto its 150,000-plus target stars, NASA oficials announced Wednesday (May 15).
But mission engineers are not conceding that Kepler’s planet-hunting days have come to an end, vowing to try their best to recover the failed reaction wheels over the coming weeks. [Gallery: A World of Kepler Planets]
“I wouldn’t call Kepler down and out just yet,” NASA science chief John Grunsfeld told reporters Wednesday.
Balky reaction wheels
The Kepler spacecraft spots exoplanets by detecting the tiny brightness dips caused when they pass in front of their parent stars from the instrument’s perspective.
The observatory needs three working reaction wheels to do such precision work. When Kepler launched in March 2009, it had four — three for immediate use and one spare.
One of the wheels, known as number two, failed in July 2012, giving Kepler no margin for error. And the loss this week of another one (called number four) puts an end to the spacecraft’s exoplanet hunt, unless a fix can be found.
Engineers have begun considering strategies for bringing the wheels back into service. They’ll likely try a light touch at times and a brute-force approach at others, officials said.
“Like with any stuck wheel that you might be familiar with on the ground, we can try jiggling it,” said Kepler deputy project manager Charlie Sobeck, of NASA’s Ames Research Center in Moffett Field, Calif. “We can try commanding it back and forth in both directions. We can try forcing it through whatever the resistance is that’s holding it up.”
It’s also possible that wheel number two will spring back to life if turned on again now, rested and restored after its long break, Sobeck and others say.
“It was putting metal on metal, and the friction was interfering with its operation, so you could see if the lubricant that is in there, having sat quietly, has redistributed itself, and maybe it will work,” Scott Hubbard of Stanford University said in a statement. (Hubbard served as director of NASA Ames during much of Kepler’s development and helped guide the mission.)
It will take a few weeks to put together a recovery plan, Sobeck said. It’s unknown if any potential fixes will do the trick, but Kepler team members are keeping their fingers crossed.
“There is a reasonable possibility that we will be able to mitigate that problem,” said mission principal investigator Bill Borucki, also of NASA Ames. “So I don’t think I’d be a pessimist here.”
There’s no chance of sending astronauts out to service Kepler, as was done five times with NASA’s Hubble Space Telescope over the years. Kepler orbits the sun rather than the Earth, and it’s currently about 40 million miles (64 million kilometers) from our planet.
Kepler has already outlasted its prime mission life of 3.5 years. And even if both reaction wheels are beyond help, Kepler’s science work may not come to an end.
It’s possible Kepler could still gather valuable data by switching to a scanning mode, as opposed to the “point and stare” operations that defined its first four years in space. If neither failed reaction wheel is recovered, NASA will carry out studies addressing possible new missions for Kepler.
It’s too soon to speculate what such missions might look like, officials said.
“We need to know more about the performance of the spacecraft before we can assess what kind of science we’ll be able to do with that performance,” Sobeck said.
More discoveries to come
Kepler has spotted more than 2,700 potential exoplanets to date. Just 132 of them have been confirmed by follow-up observations so far, but mission scientists expect that more than 90 percent will end up being the real deal.
And the flood of Kepler finds won’t slow for a while even if the instrument can no longer lock onto its target stars. The mission team has only had time to go through about half of Kepler’s enormous dataset, which team members say is certain to contain many more gems — including, possibly, the first-ever “alien Earth.”
“We have excellent data for an additional two years,” Borucki said. “So I think the most interesting, exciting discoveries are coming in the next two years. The mission is not over.”