That’s apparently what happens when a dying star swallows a smaller, dead star. And for decades, this exotic cosmic rarity was only theory, a wild idea hatched by an astronomer and a now-famous physicist and an astronomer.
It’s called a Thorne-Zytkow object (TZO), and its existence was first proposed in 1975 by physicist Kip Thorne and astronomer Anna Zytkow. TZOs The strange hybrid stars are theorized to form from binary systems containing two massive stars — a neutron star and a red supergiant star.
Neutron stars are extraordinarily dense corpses of normal stars. Red supergiants are dying stars with the greatest diameters of any star in the universe, ranging from 200 to 2,000 times wider than the sun — “so big that if you placed them where our sun is, they would extend out to, or even beyond, the orbit of Saturn,” said study lead author Emily Levesque, an astrophysicist at the University of Colorado at Boulder.
The news study, which details the likely discovery of the Thorne-Zytkow object, was published in the Sept. 1 issue of the journal MNRAS Letters. News of the find first came out, and was previewed in June, shortly after the study was submitted to the online preprint site arxiv.org.
The hunt for a hybrid star
A TZO is typically thought to form when a red supergiant engulfs an orbiting neutron star. The merger would result in “a shell of burning material around the neutron core — a shell that would generate new elements as it burned,” Thorne said in a statement. “Convection, the circulation of hot gas inside the star, would reach right into the burning shell and carry the products of burning all the way to the surface of the star long before the burning was complete.”
A TZO should appear virtually identical to a very bright red supergiant. However, a TZO’s unique innards should produce unusually large amounts of rubidium, strontium, yttrium, zirconium, molybdenum and lithium, setting it apart from a normal red supergiant.
Now, scientists have detected a red supergiant with the distinct chemical signature of a TZO, suggesting they may have detected these space oddities for the first time.
“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” Zytkow said in a June statement.
In a galaxy not so far away
The candidate TZO is named HV 2112. The star is a member of the Small Magellanic Cloud, a dwarf galaxy about 199,000 light-years away that is a close neighbor of the Milky Way and easily visible to the naked eye from the Southern Hemisphere.
The researchers identified HV 2112 after a survey of 62 red supergiants conducted with the 6.5-meter (21.3 feet) Magellan Clay telescope in Chile and the Apache Point Observatory 3.5-meter (11.5 feet) telescope in New Mexico.
“On our first night at the Magellan telescope, we had a fantastic ‘Hmmm, that’s odd’ moment,” Levesque told Space.com. “We were displaying the raw data as we took it, and when one star’s data popped up, we could tell, even in that messy format, that the spectrum was unusual. Our co-author Nidia Morrell [of the Carnegie Observatories in La Serena, Chile] looked at the data for this star and immediately said, ‘I don’t know what it is, but I know that I like it!’”
“It was our first inkling that there was something different about this star,” Levesque said. “And that star turned out to be HV 2112.”
The scientists confirmed excess levels of rubidium, molybdenum and lithium in HV 2112′s gaseous shroud.
“If HV 2112 is found to be a bona fide TZO, this would have huge implications,” Levesque said. “It could offer the first solid evidence for a completely different model of how stars’ interiors can work. Inside these stars, we also have a new way of producing elements, and knowing where the various elements come from is a critical ingredient in trying to understand how the universe works. We hear that everything is made of ‘star stuff’ — inside TZOs, we might have found a totally new way to make some of it.”
Is it really there?
The evidence that HV 2112 is a TZO is strong “but not ironclad,” Thorne said in a statement. “Certainly it’s by far the best candidate for a TZO that anyone has seen, but additional confirmation is needed.”
Although HV 2112 looks exactly how the researchers expected a TZO to look, “some of those expectations are based on models and predictions from a couple of decades ago,” Levesque said. “It’s possible that when modern-day models are run, they will give us new things to look for or new ideas of what a TZO might look like.”
Levesque noted that she had already “gotten dozens of emails from people who are interested in running their own new computer models to test how TZO interiors work, how they might form or evolve, or even whether or not they can stably exist. “A few months ago, TZOs were an interesting but somewhat obscure topic, but our discovery has spurred a renewed interest in these stars,” Levesque said. “Whether people are criticizing our findings or setting out to prove us wrong honestly matters less to me than the fact that new research on TZOs is underway — the more people study them, the more we’ll know!”
Levesque said that after she and her colleagues get more information on what modern-day models predict TZOs should look like, they would like to get more observations of HV 2112 and its surroundings “to see if there are any other strange quirks or tell-tale signs of it being a TZO.”
“Searching for more TZOs would obviously be exciting, too,” Levesque added. “Finding one is interesting, but if we find several, we’ll be able to learn so much more.”
On April 23, NASA’s Swift satellite spotted the enormous star flare coming from DG Canum Venaticorum (DG CVn), a system of two red dwarfs located about 60 light-years from Earth. The eruption put to shame anything ever seen on the sun, whose strong flares are classified into three categories, with C flares being the weakest, M of medium strength and X the most powerful.
“The biggest flare we’ve ever seen from the sun occurred in November 2003 and is rated as X45,” Stephen Drake, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. “The flare on DG CVn, if viewed from a planet the same distance as Earth is from the sun, would have been roughly 10,000 times greater than this, with a rating of about X100,000.”
For a few minutes, the superflare’s X-ray brightness outshone both stars’ total luminosity in all wavelengths, researchers said. The eruption’s temperature reached 360 million degrees Fahrenheit (200 million degrees Celsius) — about 13 times hotter than the sun’s core.
But DG CVn wasn’t done yet, firing off a number of other flares over the next 11 days, with each one being a bit weaker than the last. X-ray emission from the system finally returned to baseline levels 20 days after the April 23 event.
DG CVn’s sustained activity surprised scientists.
“We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks,” said Drake, who gave a presentation about the DG CVn superflare in August at a meeting of the American Astronomical Society’s High Energy Astrophysics Division. “This was a very complex event.”
Both of the stars in the DG CVn system are about one-third as massive as the sun. They orbit about 3 astronomical units from each other — too close for Swift to tell which one of them was responsible for the big flares this year. (One astronomical unit, or AU, is the average distance from Earth to the sun — about 93 million miles, or 150 million kilometers).
The DG CVn stars complete one rotation in less than a day, compared to about 25 days for the sun. The dwarfs’ rotational speed helps explain how they are capable of such powerful flaring, researchers said: Flares erupt when a star’s twisted magnetic fields reconnect, and rapid spin amps these fields up.
The sun may once have blasted out megaflares, too. A star’s rotational speed decreases as it ages, and our sun is middle-aged at about 5 billion years old. The DG CVn stars are just 30 million years old or so, researchers said.
In the past 20 years or so, astronomers have confirmed the existence of nearly 2,000 worlds outside Earth’s solar system. Many of these exoplanets lie in the habitable zones of stars, areas potentially warm enough for the worlds to harbor liquid water on their surfaces. Astrobiologists hope that life may someday be spotted on such alien planets, since there is life pretty much everywhere water exists on Earth.
One strategy to discover signs of such alien life involves looking for ways that organisms might change a world’s appearance. For example, chemicals typically shape what are known as the spectra seen from planets by adding or removing wavelengths of light. Alien-hunting telescopes could look for spectra that reveal chemicals associated with life. In other words, these searches would focus on biosignatures — chemicals or combinations of chemicals that life could produce, but that processes other than life could not or would be unlikely to create.
Astrophysicists Timothy Brandt and David Spiegel at the Institute for Advanced Study in Princeton, New Jersey, sought to see how challenging it might be to conclusively identify signatures of water, oxygen and chlorophyll — the green pigment that plants use to convert sunlight to energy — on a distant twin of Earth using a future off-Earth instrument such as NASA’s proposed Advanced Technology Large-Aperture Space Telescope (ATLAST).
The scientists found that water would be the easiest to detect.
“Water is a very common molecule, and I think a mission to take spectra of exoplanets should certainly look for water,” said Brandt, the lead study author. “Indeed, we have found water in a few gas giants more massive than Jupiter orbiting other stars.”
In comparison, oxygen is more difficult to detect than previously thought, requiring scientific instruments approximately twice as sensitive as those needed to detect water and significantly better at discriminating between similar colors of light.
“Oxygen, however, has only been a large part of Earth’s atmosphere for a few hundred million years,” Brandt said. “If we see it in an exoplanet, it probably points to life, but not finding oxygen certainly does not mean that the planet is sterile.”
Although a well-designed space telescope could detect water and oxygen on a nearby Earth twin, the astrophysicists found the instrument would need to be significantly more sensitive or very lucky, to see chlorophyll. Identifying this chemical typically requires scientific instruments about six times more sensitive than those needed for oxygen. Chlorophyll becomes as detectable as oxygen only when an exoplanet has a lot of vegetation and/or little in the way of cloud cover, researchers said.
Chlorophyll slightly reddens the light from Earth. If extraterrestrial life does convert sunlight to energy as plants do, scientists expect that the alien process might use a different pigment than chlorophyll. But alien photosynthesis could also slightly redden planets, just as chlorophyll does.
“Light comes in packets called photons, and only photons with at least a certain amount of energy are useful for photosynthesis,” Brandt said. Chlorophyll reflects photons that are too red and low in energy to be used for photosynthesis, and it may be reasonable to assume that extraterrestrial pigments would do the same thing, Brandt noted.
The researchers suggest a strategy for discovering Earthlike alien life that first looks for water, then oxygen on the more favorable planets and finally chlorophyll on only the most exceptionally promising worlds.
“The goal of a future space telescope will be primarily to detect water and oxygen on a planet around a nearby star,” Brandt said. “The construction and launch of such a telescope will probably cost at least $10 billion and won’t happen for at least 20 years — a lot of technology development needs to happen first — but it could be the most exciting mission of my lifetime.”
Brandt and Spiegel detailed their findings online Sept. 1 in the journal Proceedings of the National Academy of Sciences.
The molecule in question — iso-propyl cyanide (i-C3H7CN) — was spotted in Sagittarius B2, a huge star-making cloud of gas and dust near the center of the Milky Way, about 27,000 light-years from the sun. The discovery suggests that some of the key ingredients for life on Earth could have originated in interstellar space.
A specific molecule emits light at a particular wavelength and in a telltale pattern, or spectrum, which scientists can detect using radio telescopes. For this study, astronomers used the enormous Atacama Large Millimeter/submillimeter Array (ALMA) telescope in the Chilean desert, which went online last year and combines the power of 66 radio antennas. [5 Bold Claims of Alien Life]
Iso-propyl cyanide joins a long list of molecules detected in interstellar space. But what makes this discovery significant is the structure of iso-propyl cyanide. All other organic molecules that have been detected in space so far (including normal-propyl cyanide, the sister of i-C3H7CN) are made of a straight chain with a carbon backbone. Iso-propyl cyanide, however, has a “branched” structure. This same type of branched structure is a key characteristic of amino acids.
“Amino acids are the building blocks of proteins, which are important ingredients of life on Earth,” the study’s lead author, Arnaud Belloche, of the Max Planck Institute for Radio Astronomy, told Space.com in an email. “We are interested in the origin of amino acids in general and their distribution in our galaxy.”
Scientists have previously found amino acids in meteorites that fell to Earth, and the composition of these chemicals suggested they had an interstellar origin. The researchers in this new study did not find amino acids, but their discovery adds an “additional piece of evidence that the amino acids found in meteorites could have been formed in the interstellar medium,” Belloche wrote.
“The detection of a molecule with a branched carbon backbone in interstellar space, in a region where stars are being formed, is interesting because it shows that interstellar chemistry is indeed capable of producing molecules with such a complex, branched structure,” Belloche added.
It was first suggested in the 1980s that branched molecules could form on the surface of dust grains in interstellar space. But this is the first time such compounds have been detected. What’s more, iso-propyl cyanide seemed to be plentiful — it was almost half as abundant of its more common sister variant in Sagittarius B2, the study found. This means that branched molecules could actually be quite ordinary in interstellar space, the researchers said.
Researchers using data gathered by NASA’s Hubble Space Telescope have determined that the supernova SN 1993J — which was first observed in 1993, as its name suggests — occurred because one star nabbed hydrogen from another.
“This is like a crime scene, and we finally identified the robber,” study co-author Alex Filippenko, a professor of astronomy at the University of California, Berkeley, said in a statement. “The companion star stole a bunch of hydrogen before the primary star exploded.” [Supernova Photos: Great Images of Star Explosions]
One telltale sign that something was unusual came through looking at the composition of SN 1993J, which is a Type IIb supernova — a rare kind of star explosion that has much less hydrogen than typical supernovas do.
Astronomers began searching for the companion star shortly after the discovery of SN 1993J, which is found in the Messier 81 galaxy, about 11 million light-years from Earth. They were unable to find the companion, however, because the supernova zone was so crowded that it was tough to know if they were observing the correct star.
“A binary system is likely required to lose the majority of the primary star’s hydrogen envelope prior to the explosion,” said lead author Ori Fox, also of UC Berkeley. “The problem is that, to date, direct observations of the predicted binary companion star have been difficult to obtain since it is so faint relative to the supernova itself.”
What eventually turned the tide was combining optical images with Hubble ultraviolet (UV) data to find the spectrum of elements expected to emanate from the companion star. The team plans to examine the system further to find more properties of the companion and to better figure out how stars explode, researchers said.
“We were able to get that UV spectrum with Hubble. This conclusively shows that you have an excess of continuum emission in the UV, even after the light from other stars has been subtracted,” said co-author Azalee Bostroem of the Space Telescope Science Institute in Baltimore, Maryland.
While supernovas occur about once every second throughout the cosmos, catching one is a challenge to astronomers. Many of them appear faint because they are far from our planet, or they can be obscured from our view by cosmic dust. This makes predicting star explosions even more of a puzzle for scientists.
A team of researchers has delineated the “Venus Zone,” the range of distances from a host star where planets are likely to resemble Earth’s similarly sized sister world, which has been rendered unlivably hot due to a runaway greenhouse effect.
The new study should help scientists get a better handle on how many of the rocky planets spotted by NASA’s prolific Kepler space telescope are truly Earth-like, team members said.
“The Earth is Dr. Jekyll, and Venus is Mr. Hyde, and you can’t distinguish between the two based only on size,” lead author Stephen Kane, of San Francisco State University, said in a statement. “So the question then is, how do you define those differences, and how many ‘Venuses’ is Kepler actually finding?”
The results could also lead to a better understanding of Earth’s history, Kane added.
“We believe the Earth and Venus had similar starts in terms of their atmospheric evolution,” he said. “Something changed at one point, and the obvious difference between the two is proximity to the sun.”
Kane and his team defined the Venus Zone based on solar flux — the amount of stellar energy that orbiting planets receive. The outer edge of the zone is the point at which a runaway greenhouse effect would take hold, with a planet’s temperature soaring thanks to heat-trapping gases in its atmosphere. The inner boundary, meanwhile, is the distance at which stellar radiation would completely strip away a planet’s air.
The thinking is similar to that behind the “habitable zone” — the just-right range of distances from a star at which liquid water, and perhaps life as we know it, may be able to exist.
The dimensions of these astronomical zones vary from star to star, since some stars are hotter than others. In our own solar system, the Venus Zone’s outer boundary lies just inside the orbit of Earth, researchers said.
Future space-based instruments — such as NASA’s $8.8 billion James Webb Space Telescope, scheduled to launch in 2018 — will be able to analyze some exoplanets’ atmospheres, helping scientists refine the Venus Zone concept, researchers said.
“If we find all of these planets in the Venus Zone have a runaway greenhouse-gas effect, then we know that the distance a planet is from its star is a major determining factor. That’s helpful to understanding the history between Venus and Earth,” Kane said.
“This is ultimately about putting our solar system in context,” he added. “We want to know if various aspects of our solar system are rare or common.”
The Kepler spacecraft launched in March 2009 on a mission to determine how commonly Earth-like planets occur around the Milky Way galaxy. To date, Kepler has detected more than 4,200 exoplanet candidates, 978 of which have been confirmed by follow-up observations or analysis. Mission team members think about 90 percent of the candidates will eventually turn out to be the real deal.
The telescope suffered a glitch in May 2013 that ended its original exoplanet hunt, but Kepler has embarked upon a new mission called K2, which calls for it to observe a range of cosmic objects and phenomena.
The image, released today by the European Southern Observatory (ESO), shows a distant cluster of bright stars outside of the Milky Way. A related video of the globular cluster Messier 54 shows it glowing in a small satellite galaxy of the Milky Way called the Sagittarius Dwarf Galaxy about 90,0000 light-years away, according to ESO.
Messier 54′s location gives scientists a unique opportunity to study the stars of the cluster and make comparisons to those housed within the Milky Way. About 150 globular star clusters — groupings of stars that date back to the early days of the galaxy — orbit the Earth’s galaxy, ESO representatives said. [Gallery: 65 All-Time Great Galaxy Hits (Photos)]
Astronomers have found that the old stars in globular clusters of the Milky Way actually have less of the element lithium than expected.
“Most of the light chemical-element lithium now present in the universe was produced during the Big Bang, along with hydrogen and helium, but in much smaller quantities,” ESO representatives said in a statement. “Astronomers can calculate quite accurately how much lithium they expect to find in the early universe, and from this, work out how much they should see in old stars. But the numbers don’t match. There is about three times less lithium in stars than expected.”
Until now, researchers haven’t been able to measure lithium in globular clusters outside of the Milky Way for comparison, but now, with the new data collected by ESO’s VLT Survey Telescope, scientists have found that a sampling of stars in Messier 54 is also missing some lithium, according to ESO.
A group of scientists led by Alessio Mucciarelli of the University of Bologna, Italy, used the new information to find that the lithium puzzle doesn’t just affect the Milky Way. Because Messier 54 is missing a similar amount of lithium, scientists have extrapolated that the element is missing from other galaxies, as well.
Astronomers have come up with a few explanations for the strange lithium mystery.
“The first is that the calculations of the amounts of lithium produced in the Big Bang are wrong, but very recent tests suggest that this is not the case,” ESO representatives said. “The second is that the lithium was somehow destroyed in the earliest stars, before the formation of the Milky Way. The third is that some process in the stars has gradually destroyed lithium during their lives.”
Supernovas, the most powerful stellar explosions in the universe, may result from catastrophic nuclear explosions on dead stars, new research shows. Scientists had long theorized that such nuclear events cause some supernovas, but now researchers finally have direct evidence.
A supernova shines brightly enough to briefly outshine all the stars in its galaxy, making it visible from halfway across the universe. Such explosions are rare, only occurring within each galaxy about every 100 years.
For decades, scientists theorized that about one-quarter of all supernovas, a kind known as type Ia supernovas, involved white dwarfs, the remains of stars that cram the mass of the sun into a much smaller volume. White dwarfs are incredibly dense; just a teaspoon of matter from a white dwarf would weigh 5 tons. This gives the stars intense gravitational fields.
Researchers have suggested that when a white dwarf has a companion star, the white dwarf’s gravitational pull can strip matter off the nearby star. This can result in too much extra material on the white dwarf, eventually destabilizing it and setting off a thermonuclear chain reaction that explosively obliterates the white dwarf. However, until now, astronomers did not have direct evidence for this idea.
To search for such evidence and learn more about how type Ia supernovas happen, scientists investigated the supernova SN 2014J, which occurred in January. The explosion happened in a nearby galaxy called M82, located about 11.4 million light-years from Earth.
Until now, type Ia supernovas had exploded too far away for astronomers to detect any gamma rays emitted by the explosions, which made it difficult to probe some of the supernovas’ fundamental properties. However, SN 2014J is the nearest type Ia supernova to Earth detected in at least four decades, and scientists managed to analyze gamma rays from between 50 and 100 days after the explosion occurred, using the European Space Agency satellite INTEGRAL.
Exploding white dwarfs should be full of nickel-56, an unstable isotope of the element. As nickel-56 decays, its byproducts give off specific wavelengths of gamma rays. INTEGRAL detected such radiation, with the levels hinting at an amount of nickel-56 equal to about 200,000 times the mass of the Earth. This is about what scientists expect would be involved with a type Ia supernova.
These findings offer evidence that SN 2014J and other type Ia supernovas do probably originate from thermonuclear explosions on white dwarfs.
This provides an unambiguous proof of the theoretical concept behind supernova type Ias,” said study lead author Eugene Churazov, an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany.
However, astronomers have suggested another way type Ia supernovas can happen: when one white dwarf explosively collides with another. The researchers noted their findings cannot rule out the possibility of such a white-dwarf merger for SN 2014J. To confirm which mechanism actually caused SN 2014J, astronomers continue to gather data.
“The search for clues on the progenitor is underway in radio, optical and X-ray bands,” Churazov told Space.com.
The discovery of a complex microbial ecosystem far beneath the Antarctic ice may be exciting, but it doesn’t necessarily mean that life teems on frigid worlds throughout the solar system, researcher’s caution.
Scientists announced today (Aug. 20) in the journal Nature that many different types of microbes live in subglacial Lake Whillans, a body of fresh water entombed beneath 2,600 feet (800 meters) of Antarctic ice. Many of the micro-organisms in these dark depths apparently get their energy from rocks, the researchers report.
The results could have implications for the search for life beyond Earth, notes Martyn Tranter of the University of Bristol in England, who did not participate in the study. [6 Most Likely Places for Alien Life in the Solar System]
“The team has opened a tantalizing window on microbial communities in the bed of the West Antarctic Ice Sheet, and on how they are maintained and self-organize,” Tranter wrote in an accompanying “News and Views” piece in the same issue of Nature. “The authors’ findings even beg the question of whether microbes could eat rock beneath ice sheets on extraterrestrial bodies such as Mars. This idea has more traction now.”
But just how much traction is a matter of debate. For example, astrobiologist Chris McKay of NASA’s Ames Research Center in California doesn’t see much application to Mars or any other alien world.
“First, it is clear that the water sampled is from a system that is flowing through ice and out to the ocean,” said McKay, who also was not part of the study team.
“Second, and related to this, the results are not indicative of an ecosystem that is growing in a dark, nutrient-limited system,” McKay told Space.com via email. “They are consistent with debris from the overlying ice — known to contain micro-organisms — flowing through and out to the ocean. Interesting in its own right, but not a model for an isolated ice-covered ecosystem.”
Isolated, ice-covered oceans exist on some moons of the outer solar system, such as Jupiter’s moon Europa and the Saturn satellite Enceladus — perhaps the two best bets to host life beyond Earth. McKay and other astrobiologists would love to know if these oceans do indeed host life.
It may be possible to find out without even touching down on Europa or Enceladus. Plumes of water vapor spurt into space from the south polar regions of both moons, suggesting that flyby probes could sample their subsurface seas from afar.
And Europa is on the minds of the higher-ups at both NASA and the European Space Agency (ESA). NASA is drawing up plans for a potential Europa mission that could blast off in the mid-2020s, while ESA aims to launch its JUpiter ICy moons Explorer (JUICE) mission —which would study the Jovian satellites Callisto and Ganymede in addition to Europa — in 2022.
ANALYSIS: Supermassive Black Hole Jet Mystery Solved
For any given galaxy, it is estimated that a star will be destroyed by the central supermassive black hole approximately once every 10,000 years. The vast majority of known galaxies are thought to contain at least one supermassive black hole in their cores, having a dramatic effect on galactic and stellar evolution. [Images: Black Holes of the Universe]
As a star drifts too close to a supermassive black hole, intense tidal stresses rip the star to shreds. As this happens, the shredded material will be dragged into the black hole’s accretion disk — a hot disk of gas that is gradually pulled into the black hole’s event horizon, bulking up the black hole’s mass, or blasted as energetic jets from its poles.
Should there be a rapid injection of material — i.e. a star becoming blended and ingested into the accretion disk — powerful X-rays of a specific signature will be generated.
NEWS: Supermassive Black Holes are Not Doughnuts!
In a new study by the Moscow Institute of Physics and Technology and Space Research Institute of the Russian Academy of Sciences, astrophysicists trawled through observations from two space observatories to discover three likely occasions where stars have been eaten by supermassive black holes. Their work has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
Using data from the German ROSAT and European XMM-Newton space observatories, X-ray data from 1990 (to today) could be accessed and three events in different galaxies were positively identified — designated 1RXS J114727.1 + 494302, 1RXS J130547.2 + 641252 and 1RXS J235424.5-102053. Invaluable to this study was the long-duration observations by ROSAT (which operated from 1990 to 1999) and XMM-Newton (launched in 1999) that could detect the moment of stellar death, keeping track of the X-ray emissions over the years as the star’s material was gradually ingested.
NEWS: Intermediate Black Hole Implicated in Star’s Death
No more than two dozen other stellar death event candidates were seen in the observations, but positive identifications probably won’t be available until the launch of the multi-instrument Spectrum-X-Gamma space observatory in 2016.
This work has added some much needed detail to these rare events, indicating that (on average) one star every 30,000 years in any given galaxy will be destroyed by the central supermassive black hole, though the researchers caution that more observations of stars being eaten by supermassive black holes are needed.
Now, with new forensic data gathered by NASA telescopes, scientists say they have a better idea about what caused the star explosion in the nearby Messier 82 galaxy.
At 12 million light-years away, the Type Ia supernova first spotted on Jan. 21 was the closest to Earth in years. There are two primary explanations for how Type Ia supernovas are triggered: Either a small dense star core known as a white dwarf takes on too much mass from its companion star, or two white dwarfs merge. Both result in a spectacular explosion. But that first scenario should enshroud the white dwarf in a cloud of gas that produces a significant amount of X-rays after the explosion. The second would leave little or no X-rays behind.
A group of astronomers looked for an X-ray source around the supernova in Messier 82, also known as the Cigar Galaxy, using NASA’s Swift telescope and Chandra X-ray Observatory. But their search turned up quite empty. Compared with older data gathered around the region, there were no new X-rays present after the supernova.
“While it may sound a bit odd, we actually learned a great deal about this supernova by detecting absolutely nothing,” study leader Raffaella Margutti of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, said in a statement from NASA. “Now we can essentially rule out that the explosion was caused by a white dwarf continuously pulling material from a companion star.”
Margutti and colleagues say more work is still needed to confirm how the supernova named SN 2014J was triggered.
Black holes do indeed come in three sizes: small, medium and extra large, a new study suggests.
Astronomers have studied many black holes at either size extreme — “stellar-mass” black holes, which are a few dozen times as weighty as the sun, and supermassive black holes, which can contain millions or billions of times the mass of the sun and lurk at the heart of most, if not all, galaxies.
Researchers have spotted hints of much rarer medium-size black holes, which harbor between 100 and several hundred thousand solar masses. But it’s tough to weigh these objects definitively — so tough that their existence has been a matter of debate.
But that debate can now be put to rest, says a research team that has measured an intermediate black hole’s mass with unprecedented precision. A black hole in the nearby galaxy M82 weighs in at 428 solar masses, give or take a hundred suns or so, they report today (Aug. 17) in the journal Nature.
“Objects in this range are the least expected of all black holes,” study co-author Richard Mushotzky, an astronomy professor at the University of Maryland, said in a statement. “Astronomers have been asking, ‘Do these objects exist, or do they not exist? What are their properties?’ Until now, we have not had the data to answer these questions.”
Patterns in the light
Black holes famously gobble up anything that gets too close, including light. But that doesn’t mean astronomers can’t see them; bright X-ray light streams from the superhot disk of material spiraling into a black hole’s mouth.
About 15 years ago, NASA’s Chandra X-ray Observatory spacecraft spotted such emissions coming from a source in the galaxy M82, which lies about 12 million light-years away from Earth. For a long time, Mushotzky and some other scientists suspected that the object, called M82 X-1, was a medium-size black hole. But those suspicions were tough to confirm.
“For reasons that are very hard to understand, these objects have resisted standard measurement techniques,” Mushotzky said.
In the new study, a team led by University of Maryland doctoral student Dheeraj Pasham took a closer look at M82 X-1. They studied observations made from 2004 to 2010 by NASA’s Rossi X-ray Timing Explorer (RXTE) satellite, which ceased operations in 2012.
The RXTE data revealed a pair of repeating oscillations in M82 X-1′s X-ray emissions. These oscillations occurred 5.1 times per second and 3.3 times per second, respectively — a ratio of three to two. This fact allowed the team to determine the black hole’s mass.
“In essence, [the] frequency of these 3:2 ratio oscillations scales inverse[ly] with black hole mass,” Pasham told Space.com via email. “Simply put, if the black hole is small, the orbital periods at the innermost circular orbit are shorter, but if the black hole is big, the orbital periods are longer (smaller frequencies).”
The researchers calculated M82 X-1′s mass at 428 suns, plus or minus 105 solar masses.
“In our opinion, and as the paper’s referees seem to agree, this is the most accurate mass measurement of an intermediate-mass black hole to date,” Pasham said.
Learning about black-hole growth
Confirming the existence of intermediate black holes could help researchers better understand the supermassive monsters at the cores of galaxies.
Such behemoths apparently first formed in the universe’s very early days, just a few hundred million years after the Big Bang. They could not have grown so big so fast if their “seeds” were small stellar-mass black holes (which result from the collapse of giant stars), Pasham said.
“Many theories, therefore, have suggested that these initial seed black holes had to have been a few 100 -1,000 times our sun,” he said. “But we did not have firm evidence for such intermediate-mass black holes.”
Stellar-mass black holes also often feature paired X-ray oscillations that occur in a 3:2 frequency ratio. Therefore, the new observations suggest that medium-size black holes may behave like scaled-up versions of stellar-mass black hole systems, Pasham added.
These compounds may reveal that extraterrestrials have disastrously altered their planets, scientists added.
To detect biomarkers, or signs of life, on distant worlds, scientists have often focused on molecules such as oxygen, which theoretically disappears quickly from atmospheres unless life is present to provide a constant supply of the gas. By looking at light passing through atmospheres of alien worlds, past studies have suggested future instruments such as NASA’s James Webb Space Telescope could detect telltale traces of oxygen.
But the search for extraterrestrial intelligence (SETI) has mostly concentrated on “technosignatures,” such as radio and other electromagnetic signals that alien civilizations might give off. Now researchers suggest that searches for atmospheric biomarkers could also look for industrial pollutants as potential signs of intelligent aliens.
Astronomers at Harvard University focused on tiny, superdense stars known as white dwarfs. More than 90 percent of all stars in the Milky Way, including our own sun, will one day end up as white dwarfs, which are made up of the dim, fading cores of stars.
Though white dwarfs are quite cold for stars, they would still be warm enough to possess so-called habitable zones — orbits where liquid water can exist on the surfaces of circling planets. These zones are considered potential habitats for life, as there is life virtually everywhere there is liquid water on Earth.
The scientists examined how Earth-size planets in the habitable zones of white dwarfs might look if they possessed industrial pollutants in their atmosphere. They focused on chlorofluorocarbons (CFCs), which are entirely artificial compounds, with no known natural process capable of creating them in atmospheres.
CFCs are nontoxic chemicals that were once used in hairspray and air conditioners, among many other products, before researchers discovered they were causing a hole in Earth’s ozone layer, which protects the planet from dangerous ultraviolet radiation.
“Very hairy extraterrestrials may be a little easier to detect,” joked lead study author Henry Lin, a physicist at Harvard.
CFCs are strong greenhouse gases, meaning they are very effective at absorbing heat. This means that if CFCs are in the atmosphere of a distant Earth-size planet, they could alter a white dwarf’s light when that world passes in front of that star — enough for the $8.8 billion James Webb Space Telescope (JWST), which is due to launch in 2018, to detect them.
In addition, the researchers noted that CFCs are long-lived molecules, capable of lasting up to about 100,000 years in atmospheres. This means they could even serve as markers of long-dead alien civilizationsThe investigators simulated the amount of time it would take JWST to detect the fluorocarbon CF4 and the chlorofluorocarbon CCl3F in the atmosphere of an Earth-size planet in the habitable zone of a white dwarf. They modeled concentrations of these gases 100 times greater than the highs currently seen on Earth.
The scientists found it would take JWST three days of looking at such a white dwarf to detect signs of CF4, and only a day and a half for CCl3F.
“The most exciting aspect of the results is that within the next decade we might be able to search for excessive industrial pollution in the atmospheres of Earth-like planets,” study co-author Abraham Loeb, a theoretical astrophysicist and chair of Harvard’s astronomy department, told Space.com.
Ironically, “aliens are often referred to as green little creatures, but ‘green’ also means ‘environmentally friendly,’” Loeb said. “Detectable CFC-rich civilizations would not be ‘green.’”
The scientists did caution that it would take much longer to detect these industrial pollutants than it would biomarkers such as oxygen, which JWST could find after about three hours of looking at such a planet. Astronomers should only attempt to discover technosignatures such as CFCs if initial searches for fundamental biomarkers like oxygen were successful, the research team suggested.
The astronomers cautioned it would be 100 times more difficult to detect industrial pollutants on planets orbiting yellow dwarf stars like the sun, making such searches beyond the capabilities of JWST. It would also take an unrealistically long time to detect CFC levels on alien planets that match those currently found on Earth, Loeb said.
One potentially sobering future discovery might be of alien worlds that possess long-lived industrial pollutants such as CFCs but no longer have any short-lived biomarkers such as oxygen.
“If we find graveyards of other civilizations, most rational people would likely get engaged in protecting the Earth from a similar catastrophe,” Loeb said.
“We call industrial pollution a biomarker for intelligent life, but perhaps a civilization much more advanced than us with their own exoplanet program will classify industrial pollution as a biomarker for unintelligent life,” Lin said.
However, if astronomers discover a world heavy with CFCs that exists outside the habitable zone of its star, that could mean an extraterrestrial civilization may have intentionally “terraformed” that planet, making it livably warmer “by polluting it with greenhouse gases,” Loeb said. Scientists have previously suggested terraforming Mars by warming and thickening the Red Planet’s atmosphere so that humans can roam its surface without having to wear spacesuits.
The agency’s Nuclear Spectroscopic Telescope Arrayprobe, or NuSTAR, looked on as a mysterious X-ray source, called a corona, moved closer to a supermassive black hole. The black hole’s immense gravity pulled harder on the corona the closer it came, stretching and blurring the X-ray light in the process, researchers said.
“The corona recently collapsed in toward the black hole, with the result that the black hole’s intense gravity pulled all the light down onto its surrounding disk, where material is spiraling inward,” study lead author Michael Parker, of the Institute of Astronomy in Cambridge, England, said in a statement.
NuSTAR’s observations provide the most detailed look yet at such events, researchers said.
While light cannot escape once it passes the “event horizon” of a black hole, high-energy emissions do stream from the vicinity of these objects — from the corona, for example, and from the superhot disk of material spiraling into a black hole’s maw.
Astronomers think supermassive black holes — which can contain millions or billions of times the mass of the sun — reside at the cores of most, if not all, galaxies. The black hole observed by NuSTAR, called Markarian 335 (Mrk 335), is 10 million times more massive than the sun and lies 324 million light-years away, researchers said.
NASA’s Swift satellite recently observed a change in Mrk 335′s X-ray brightness, so scientists pointed NuSTAR at the supermassive black hole to take a closer look.
NuSTAR’s observations revealed that the black hole’s gravity pulled the coronal X-ray light onto the inner regions of Mrk 335′s accretion disk. Further study has shown that the corona remains close to the black hole, months after it originally moved inward. (This inward migration was rapid, occuring over a period of days rather than weeks or months, researchers said.)
The new study could shed light on the nature of black hole coronas and the extreme conditions near the cores of supermassive black holes, NASA officials said.
“We still don’t understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein’s theory of general relativity become prominent,” said co-author and NuSTAR principal investigator Fiona Harrison, of the California Institute of Technology in Pasadena.
“NuSTAR’s unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity,” she added.
Black holes may have grown incredibly rapidly in the newborn universe, perhaps helping explain why they appear so early in cosmic history, researchers say.
Black holes possess gravitational pulls so powerful that not even light can escape their clutches. They are generally believed to form after massive stars die in gargantuan explosions known as supernovas, which crush the remaining cores into incredibly dense objects.
Supermassive black holes millions to billions of times the mass of the sun occur at the center of most, if not all, galaxies. Such monstrously large black holes have existed since the infancy of the universe, some 800 million years or so after the Big Bang. However, it remains a mystery how these giants could have grown so big in the relatively short amount of time they had to form. [Images: Black Holes of the Universe]
In modern black holes, features called accretion disks limit the speed of growth. These disks of gas and dust that swirl into black holes can prevent black holes from growing rapidly in two different ways, researchers say. First, as matter in an accretion disk gets close to a black hole, traffic jams occur that slow down any other infalling material. Second, as matter collides within these traffic jams, it heats up, generating energetic radiation that drives gas and dust away from the black hole.
“Black holes don’t actively suck in matter — they are not like vacuum cleaners,” said lead study author Tal Alexander, an astrophysicist at the Weizmann Institute of Science in Rehovot, Israel.
“A star or a gas stream can be on a stable orbit around a black hole, exactly as the Earth revolves around the sun, without falling into it,” Alexander told Space.com. “It is actually quite a challenge to think of efficient ways to drive gas into the black hole at a high enough rate that can lead to rapid growth.”
Alexander and his colleague Priyamvada Natarajan may have found a way in which early black holes could have grown to supermassive proportions — in part, by operating without the restrictions of accretion disks. The pair detailed their findings online today (Aug. 7) in the journal Science.
The scientists began with a model of a black hole 10 times the mass of the sun embedded in a cluster of thousands of stars. They fed the simulated black hole continuous flows of dense, cold, opaque gas.
“The early universe was much smaller and hence denser on average than it is today,” Alexander said.
This cold, dense gas would have obscured a substantial amount of the energetic radiation given off by matter falling into the black hole. In addition, the gravitational pull of the many stars around the black hole “causes it to zigzag randomly, and this erratic motion prevents the formation of a slowly draining accretion disk,” Alexander said. This means that matter falls into the black hole from all sides instead of getting forced into a disk around the black hole, from which it would swirl in far more slowly.
The “supra-exponential growth” observed in the model black hole suggests that a black hole 10 times the mass of the sun could have grown to more than 10 billion times the mass of the sun by just 1 billion years after the Big Bang, researchers said.
“This theoretical result shows a plausible route to the formation of supermassive black holes very soon after the Big Bang,” Alexander said.
Future research could examine whether supra-exponential growth of black holes could occur in modern times as well. The high-density and high-mass cold flows seen in the ancient universe may exist “for short times in unstable, dense, star-forming clusters, or in dense accretion disks around already-existing supermassive black holes,” Alexander said.