Posted on by Shannon Hall

When do Black Holes Become Active? The Case of the Strangely-Shaped Galaxy Mrk 273

Mrk 273 as seen by the Hubble Space Telescope.

The Hubble image above shows a strange galaxy, known as Mrk 273.  The odd shape – including the infrared bright center and the long tail extending into space for 130 thousand light-years – is strongly indicative of a merger between galaxies.

Near-infrared observations have revealed a nucleus with multiple components, but for years the details of such a sight have remained obscured by dust. With further data from the Keck Telescope, based in Hawaii, astronomers have verified that this object is the result of a merger between galaxies, with the infrared bright center consisting of two active galactic nuclei – intensely luminous cores powered by supermassive black holes.

At the center of every single galaxy is a supermassive black hole. While the name sounds exciting, our supermassive black hole, Sgr A* is pretty quiescent.  But at the center of every early galaxy looms the opposite: an active galactic nuclei (AGN for short). There are plenty of AGN in the nearby Universe as well, but the question stands: how and when do these black holes become active?

In order to find the answer astronomers are looking at merging galaxies. When two galaxies collide, the supermassive black holes fall toward the center of the merged galaxy, resulting in a binary black hole system. At this stage they remain quiescent black holes, but are likely to become active soon.

“The accretion of material onto a quiescent black hole at the center of a galaxy will enable it to grow in size, leading to the event where the nucleus is “turned on” and becomes active,” Dr. Vivian U, lead author on the study, told Universe Today. “Since galaxy interaction provides means for gaseous material in the progenitor galaxies to lose angular momentum and funnels toward the center of the system, it is thought to play a role in triggering AGN.  However, it has been difficult to pinpoint exactly how and when in a merging system this triggering occurs.”

While it has been known that an AGN can “turn on” before the final coalescence of the two black holes, it is unknown as to when this will happen. Quite a few systems do not host dual AGN.  For those that do, we do not know whether synchronous ignition occurs or not.

Mrk 273 provides a powerful example to study. The team used near-infrared instruments on the Keck Telescope in order to probe past the dust.  Adaptive optics also removed the blurring affects caused by the Earth’s atmosphere, allowing for a much cleaner image – matching the Hubble Space Telescope, from the ground.

“The punch line is that Mrk 273, an advanced late-stage galaxy merger system, hosts two nuclei from the progenitor galaxies that have yet to fully coalesce,” explains Dr. U. The presence of two supermassive black holes can be easily discerned from the rapidly rotating gas disks that surround the two nuclei.

“Both nuclei have already been turned on as evidenced by collimated outflows (a typical AGN signature) that we observe” Dr. U told me. Such a high amount of energy released from both supermassive black holes suggests that Mrk 273 is a dual AGN system. These exciting results mark a crucial step in understanding how galaxy mergers may “turn on” a supermassive black hole.

The team has collected near-infrared data for a large sample of galaxy mergers at different merging states.  With the new data set, Dr. U aims “to understand how the nature of the nuclear star formation and AGN activity may change as a galaxy system progresses through the interaction.”

The results will be published in the Astrophysical Journal (preprint available here).

 

Posted on by Fraser Cain

Weekly Space Hangout – Aug. 16, 2013

Like your space news, but you just can’t handle reading any more? Then watch our Weekly Space Hangout, where we give you a rundown of all the big space news stories that broke this week.

Host: Fraser Cain

Panel: Brian Koberlein, David Dickinson, Nancy Atkinson, Nicole Gugliucci

Stories:
CIA Comes Clean About Area 51
Elon Musk’s Hyperloop
Space Fence Shut Down
Magnetar Discovered Near the Galactic Core
IAU Updates Their Naming Policy
Bright Nova in Delphinus

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern as a live Google+ Hangout on Air. Join us live on YouTube, or you can listen to the audio after the fact on the 365 Days of Astronomy Podcast.

Posted on by Elizabeth Howell

Star’s Dying Gasp May Signal Black Hole’s Birth

Where is the Nearest Black Hole
Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)

A distinctive flash of light emanating from a dying star may make it possible for astronomers to watch a black hole being born, according to new research.

This burst of light, which might last three to 10 days, could be visible in optical light and also in infrared, which shows the heat signature of cosmic objects. While not as bright as a supernova — an exploding star — this signal could occur somewhere in the sky as often as once a year, according to simulations performed at the California Institute of Technology.

“That flash is going to be very bright, and it gives us the best chance for actually observing that this event occurred,” stated Caltech postdoctoral scholar Tony Piro, who led the research that is published in Astrophysical Journal Letters. “This is what you really want to look for.”

A big star essentially turns into a black hole when it falls into itself due to its large mass. The collapse shoots out protons and electrons from the core, creating neutrons and temporarily turning the core into a neutron star (a really, really dense object). This process also makes up neutrinos, which are infinitesimal but also extremely fast, moving nearly as fast as light does and bleeding the star of energy.

Combining observations done with ESO's Very Large Telescope and NASA's Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. The black hole blows a huge bubble of hot gas, 1,000 light-years across or twice as large and tens of times more powerful than the other such microquasars. The stellar black hole belongs to a binary system as pictured in this artist's impression. Credit: ESO/L. Calçada
Combining observations done with ESO’s Very Large Telescope and NASA’s Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. The black hole blows a huge bubble of hot gas, 1,000 light-years across or twice as large and tens of times more powerful than the other such microquasars. The stellar black hole belongs to a binary system as pictured in this artist’s impression. Credit: ESO/L. Calçada

A 1980 paper, CalTech stated, showed that “this rapid loss of mass means that the gravitational strength of the dying star’s core would abruptly drop.” Hydrogen-filled layers at the top of the star would then fall outward and create a shock wave moving at more than two million miles an hour.

More recently, astronomers at the University of California, Santa Cruz discovered that the shock wave’s friction against the gas would heat up the plasma and make it glow, potentially for as long as a year. But that would be very faint from Earth-borne telescopes.

This is where the new CalTech research comes in. The university is already involved in black hole research, including the Nuclear Spectroscopic Telescope Array (NuSTAR). You can check out a video about NuSTAR below.

Piro’s simulations focus on when shock waves hit the surface of the star. It’s this process that would produce a burst of light, perhaps 10 to 100 times brighter than the other glow that astronomers foresaw.

The next step will be trying to observe these events as soon as they happen. Caltech advertised several survey possibilities related to its research: the Palomar Transient Factory, the  intermediate Palomar Transient Factory that started work in February and the even more advanced Zwicky Transient Facility (ZTF) that  is expected to start up in 2015.

Of course, it’s quite possible that other telescopes on the ground or orbit could work to confirm this signal.

Source: California Institute of Technology

Posted on by Nancy Atkinson

Astronomers Watch as a Black Hole Eats a Rogue Planet

Screen capture from the ESA video.

In Star Wars, the Millennium Falcon narrowly escaped being devoured by an exogorth (space slug) slumbering inside an asteroid crater. An unsuspecting rogue giant planet wasn’t as lucky. Astronomers using the Integral space observatory were able to watch as the planet was eaten by a black hole that had been inactive for decades. It woke up just in time to make a meal out of the unwary planet.

“The observation was completely unexpected, from a galaxy that has been quiet for at least 20–30 years,” says Marek Nikolajuk of the University of Bialystok, Poland, lead author of the paper in Astronomy & Astrophysics.

Nikolajuk and his team added that the event is a preview of a similar feeding event that is expected to take place with the black hole at the center of our own Milky Way Galaxy.

The discovery in galaxy NGC 4845, 47 million light-years away, was made by Integral, with follow-up observations from ESA’s XMM-Newton, NASA’s Swift and Japan’s MAXI X-ray monitor on the International Space Station.

Astronomers were using Integral to study a different galaxy when they noticed a bright X-ray flare coming from another location in the same wide field-of-view. Using XMM-Newton, the origin was confirmed as NGC 4845, a galaxy never before detected at high energies.

Along with Swift and MAXI, the emission was traced from its maximum in January 2011, when the galaxy brightened by a factor of a thousand, and then as it subsided over the course of the year.

By analyzing the characteristics of the flare, the astronomers could determine that the emission came from a halo of material around the galaxy’s central black hole as it tore apart and fed on an object of 14–30 Jupiter masses, and so the astronomers say the object was either a super-Jupiter or a brown dwarf.

This object appears to have been ‘wandering,’ which would fit the description of recent studies that have suggested that free-floating planetary-mass objects of this kind may occur in large numbers in galaxies, ejected from their parent solar systems by gravitational interactions.

The black hole in the center of NGC 4845 is estimated to have a mass of around 300,000 times that of our own Sun. The astronomers said it also appears to enjoy playing with its food: the way the emission brightened and decayed shows there was a delay of 2–3 months between the object being disrupted and the heating of the debris in the vicinity of the black hole.

“This is the first time where we have seen the disruption of a substellar object by a black hole,” said co-author Roland Walter of the Observatory of Geneva, Switzerland. “We estimate that only its external layers were eaten by the black hole, amounting to about 10% of the object’s total mass, and that a denser core has been left orbiting the black hole.”

The flaring event in NGC 4845 might be similar to what is expected to happen with the supermassive black hole at the center of our own Milky Way Galaxy, perhaps even this year, when an approaching Earth-mass gas cloud is expected to meet its demise.

Along with the object seen being eaten by the black hole in NGC 4845, these events will tell astronomers more about what happens to the demise of different types of objects as they encounter black holes of varying sizes.

“Estimates are that events like these may be detectable every few years in galaxies around us, and if we spot them, Integral, along with other high-energy space observatories, will be able to watch them play out just as it did with NGC 4845,” said Christoph Winkler, ESA’s Integral project scientist.

The team’s paper: Tidal disruption of a super-Jupiter in NGC 4845

Source: ESA

Posted on by John Williams

Combining Light to Reveal Monster Black Holes

NGC 3627 glows in the combined light of Hubble, Chandra, Spitzer and the Very Large Telescope in this image. Astronomers conducted a survey of 62 galaxies, including NGC 3627 to study monster black holes at their centers.

It’s not just pretty, it’s science. Like a starry watercolor, astronomers combining light from Earth and space-based observatories found 37 new supermassive black hole candidates lurking in nearby galaxies.

Included in that survey is NGC 3627 pictured above. Astronomers combined X-ray data from NASA’s Chandra X-ray Observatory, infrared data from the Spitzer Space Telescope, and optical data from the Hubble Space Telescope and the Very Large Telescope. The other images give the galaxy context but it’s the ghostly blue images from Chandra that show super bright in the X-ray images; X-ray light powered by material falling into a monster black hole.

Gas and dust slowly spins around the black hole creating a flattened disk, or accretion disk. As material falls inward, it heats up and releases large amounts of energy that shine brightly in the ultraviolet region of the spectrum.

NGC 3627, located about 30 million light-years from Earth, was just one of a survey of 62 nearby galaxies using archived data from Chandra and data from the Spitzer Infrared Nearby Galaxy Survey. Of those, 37 galaxies contained bright X-ray sources, indicating active black holes at their cores. Scientists believe that seven of those sources are new supermassive black hole candidates.

The paper describing the survey results was published in the April 10, 2011 issue of The Astrophysical Journal.

Combining ultraviolet and infrared observations confirm previous Chandra results that found that there may be many more galaxies powered by monster black holes than believed previously through optical surveys. Scientists say in the paper that low-levels of black hole activity previously may have been hidden by dust or washed out by the bright light of the galaxy.

Image caption: Bright X-ray sources glow a ghostly blue in this image in NGC 3627 from NASA’s Chandra X-ray Observatory. A study confirms previous Chandra results that indicate that more galaxies powered by monster black holes populate the cosmos.

Source: Chandra X-ray Observatory website

Posted on by Nancy Atkinson

The Milky Way’s Black Hole Shoots Out Brightest Flare Ever

This false-color image shows the central region of our Milky Way Galaxy as seen by Chandra. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy.
Image: NASA/MIT/F. Baganoff et al.

For some unknown reason, the black hole at the center of the Milky Way galaxy shoots out an X-ray flare about once a day. These flares last a few hours with the brightness ranging from a few times to nearly one hundred times that of the black hole’s regular output. But back in February 2012, astronomers using the Chandra X-Ray Observatory detected the brightest flare ever observed from the central black hole, also known as Sagittarius A*. The flare, recorded 26,000 light years away, was 150 times brighter than the black hole’s normal luminosity.

What causes these outbursts? Scientists aren’t sure. But Sagittarius A* doesn’t seem to be slowing down, even though as black holes age they should show a decrease in activity.

Mysterious X-ray flares caught by Chandra may be asteroids falling into the Milky Way's giant black hole. Credit: X-ray: NASA/CXC/MIT/F. Baganoff et al.; Illustrations: NASA/CXC/M.Weiss

Earlier this year, a group of researchers said that the outbursts may come from asteroids or even wandering planets that come too close to the black hole and they get consumed. Basically, the black hole is eating asteroids and then belching out X-ray gas.

Astronomers involved in this new observation seem to concur with that line of thinking.

“Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” said Michael Nowak, a research scientist at MIT Kavli and co-author of a new paper in the Astrophysical Journal. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”

Astronomers detect black holes by the light energy given off as they swallow nearby matter. The centers of newborn galaxies and quasars can appear extremely bright, giving off massive amounts of energy as they devour their surroundings. As black holes age, they tend to slow down, consuming less and appearing fainter in the sky.

“Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything,” says Frederick K. Baganoff, another co-author from MIT. “But in this really low-accretion-rate state, they’re really finicky eaters, and for some reason they actually blow away most of the energy.”

While such events like this big blast appear to be relatively rare, Nowak suspects that flare-ups may occur more frequently than scientists expect. The team has reserved more than a month of time on the Chandra Observatory to study Sagittarius A* in hopes of identifying more flares, and possibly what’s causing them.

“These bright flares give information on the flaring process that isn’t available with the weaker ones, such as how they fluctuate in time during the flare, how the spectrum changes, and how fast they rise and fall,” said Mark Morris from UCLA. “The greatest importance of this bright flare may be that it builds up the statistics on the characteristics of strong flares that can eventually be used to [identify] the cause of such flares.”

Even more intriguing to Baganoff is why the black hole emits so little energy. In 2003, he ran the very first observations with the then-new Chandra Observatory, and calculated that, given the amount of gas in its surroundings, Sagittarius A* should be about a million times brighter than it is — a finding that suggested the black hole throws away most of the matter it would otherwise consume.

The physics underlying such a phenomenon remain a puzzle that Baganoff and others hope to tease out with future observations.

“We’re really studying the great escape, because most of the gas escapes, and that’s not what we expect,” Baganoff says. “So we’re piecing out the history of the activity of the center of our galaxy.”

Paper: Chandra/HETGS Observations of the Brightest Flare seen from Sgr A*

See a movie of the flare here.

Source: MIT

Posted on by John Williams

Stirred, Not Shaken. Black Hole Antics Puff Up Whopper of a Galaxy

Its massive gravitational field warping space, the huge elliptical galaxy A2261-BCG, seems to have a diffuse halo of stars instead of a bright central galactic core. Image credit: NASA/ESA Hubble

Bloated far beyond the size of normal galaxies, one or more black holes may have puffed up an elliptical galaxy to a whopping size, according to astronomers. To their surprise, however, the black holes are missing.

Normally, scientists measure a concentrated peak of light surrounding the central black hole surrounded by a fuzzy halo of stars. Instead, astronomers, using NASA’s Hubble Space Telescope, find that the galaxy, known as A2261-BCG, is just a diffuse, bloated foggy patch of light. The intensity of starlight remains even across the entire galaxy. Past Hubble observations show supermassive black holes, each weighing billions of times more than our Sun, reside at the cores of nearly all galaxies.

“Expecting to find a black hole in every galaxy is sort of like expecting to find a pit inside a peach,” explained astronomer and co-author Tod Lauer in a press release. Lauer is with the National Optical Astronomy Observatory in Tucson, Ariz. “With this Hubble observation, we cut into the biggest peach and we can’t find the pit. We don’t know for sure that the black hole is not there, but Hubble shows that there’s no concentration of stars in the core.”

So where are the black holes?

Astronomers, in a paper that appeared in the September 10 issue of The Astrophysical Journal, have two ideas, both involving galactic billiards, for the galaxy’s puffy appearance. In one scenario, a pair of merging black holes gravitationally stir up then scatter the galaxy’s stars. In another, the merging black holes are ejected leaving the swarm of stars with no gravitational anchor allowing them to wander outward.

Galaxy cores tend to be sized proportionally to the wheeling expanse of the host galaxy. In the case of A2261-BCG, which spans about a million light-years (10 times that of our Milky Way Galaxy), the central region is three times larger than other very luminous galaxies, according to the paper. The monster galaxy is the most massive and brightest galaxy in the Abell 2261 galaxy cluster.

Team leader Marc Postman of the Space Telescope Science Institute in Baltimore, Md., said in the press release that the galaxy stood out in the Hubble image. “When I first saw the image of this galaxy, I knew right away it was unusual,” Postman explained. “The core was very diffuse and very large. The challenge was then to make sense of all the data, given what we knew from previous Hubble observations, and come up with a plausible explanation for the intriguing nature of this particular galaxy.”

The team admits the ejected black-hole ideas sound far-fetched, “but that’s what makes observing the universe so intriguing — sometimes you find the unexpected,” said Postman.

As a follow-up, the team is searching for the sound of material falling into the black hole using the Very Large Array (VLA) radio telescope in New Mexico. Comparing the VLA data with Hubble images will allow the researchers to confirm the existence of a black hole and map its location.

Source: Hubblesite

Posted on by Nancy Atkinson

Astronomers Find Ultimate Oxymoron: A Small Supermassive Black Hole

There’s jumbo shrimp and accurate rumors; now there’s even a mini supermassive black hole. Astronomers have identified the smallest supermassive black hole ever observed, and while it’s considered a shrimp as far as supermassive black holes go, this guy is still pretty big: the mass of the black hole in galaxy NGC 4178 is estimated to be about 200,000 times the mass of our Sun. But it was a surprise that this galaxy had a black hole at all.

Astronomers using the Chandra X-Ray Observatory in conjunction with other observatories took a look at NGC 4178, a late-type spiral galaxy located about 55 million light years from Earth. It does not contain a bright central concentration, or bulge, of stars in its center, and so it was thought that perhaps this galaxy was one of the few that didn’t harbor a black hole.

With using Chandra’s X-Ray vision, as well as infrared data the NASA’s Spitzer Space Telescope and radio data from the Very Large Array, Nathan Secrest, from George Mason University and his team identified a weak X-ray source at the center of the galaxy, and also saw varying brightness at infrared wavelengths, suggesting that a black hole was actually in the center of NGC 4178 and was pulling in material from its surroundings. The same data also suggested that light generated by this infalling material is heavily absorbed by gas and dust and was therefore surrounding a black hole.

They were able to estimate the size of the black hole by using the known relationship between the mass of a black hole and the amount of X-rays and radio waves it generates.

While this is the lowest mass supermassive black holes ever observed, astronomers admit this is probably near the extreme low-mass end of being in the “supermassive” range. And as the team pointed out in their paper, there is increasing evidence that several late-type galaxies do host supermassive black holes, and that a classical bulge is not a requirement for a supermassive black hole to form and grow.

Read the team’s paper.

Source: NASA

Posted on by Jenny Winder

Integral: Ten Years Tracking Extreme Radiation Across the Universe

Caption: Artist’s impression of ESA’s orbiting gamma-ray observatory Integral. Image credit: ESA

Integral, ESA’s International Gamma-Ray Astrophysics Laboratory launched ten years ago this week. This is a good time to look back at some of the highlights of the mission’s first decade and forward to its future, to study at the details of the most sensitive, accurate, and advanced gamma-ray observatory ever launched. But the mission has also had some recent exciting research of a supernova remnant.

Integral is a truly international mission with the participation of all member states of ESA and United States, Russia, the Czech Republic, and Poland. It launched from Baikonur, Kazakhstan on October 17th 2002. It was the first space observatory to simultaneously observe objects in gamma rays, X-rays, and visible light. Gamma rays from space can only be detected above Earth’s atmosphere so Integral circles the Earth in a highly elliptical orbit once every three days, spending most of its time at an altitude over 60 000 kilometres – well outside the Earth’s radiation belts, to avoid interference from background radiation effects. It can detect radiation from events far away and from the processes that shape the Universe. Its principal targets are gamma-ray bursts, supernova explosions, and regions in the Universe thought to contain black holes.

5 metres high and more than 4 tonnes in weight Integral has two main parts. The service module is the lower part of the satellite which contains all spacecraft subsystems, required to support the mission: the satellite systems, including solar power generation, power conditioning and control, data handling, telecommunications and thermal, attitude and orbit control. The payload module is mounted on the service module and carries the scientific instruments. It weighs 2 tonnes, making it the heaviest ever placed in orbit by ESA, due to detectors’ large area needed to capture sparse and penetrating gamma rays and to shield the detectors from background radiation in order to make them sensitive. There are two main instruments detecting gamma rays. An imager producing some of the sharpest gamma-ray images and a spectrometer that gauges gamma-ray energies very precisely. Two other instruments, an X-ray monitor and an optical camera, help to identify the gamma-ray sources.

During its extended ten year mission Integral has has charted in extensive detail the central region of our Milky Way, the Galactic Bulge, rich in variable high-energy X-ray and gamma-ray sources. The spacecraft has mapped, for the first time, the entire sky at the specific energy produced by the annihilation of electrons with their positron anti-particles. According to the gamma-ray emission seen by Integral, some 15 million trillion trillion trillion pairs of electrons and positrons are being annihilated every second near the Galactic Centre, that is over six thousand times the luminosity of our Sun.

A black-hole binary, Cygnus X-1, is currently in the process of ripping a companion star to pieces and gorging on its gas. Studying this extremely hot matter just a millisecond before it plunges into the jaws of the black hole, Integral has discovered that some of it might be escaping along structured magnetic field lines. By studying the alignment of the waves of high-energy radiation originating from the Crab Nebula, Integral found that the radiation is strongly aligned with the rotation axis of the pulsar. This implies that a significant fraction of the particles generating the intense radiation must originate from an extremely organised structure very close to the pulsar, perhaps even directly from the powerful jets beaming out from the spinning stellar core.

Just today ESA reported that Integral has made the first direct detection of radioactive titanium associated with supernova remnant 1987A. Supernova 1987A, located in the Large Magellanic Cloud, was close enough to be seen by the naked eye in February 1987, when its light first reached Earth. Supernovae can shine as brightly as entire galaxies for a brief time due to the enormous amount of energy released in the explosion, but after the initial flash has faded, the total luminosity comes from the natural decay of radioactive elements produced in the explosion. The radioactive decay might have been powering the glowing remnant around Supernova 1987A for the last 20 years.

During the peak of the explosion elements from oxygen to calcium were detected, which represent the outer layers of the ejecta. Soon after, signatures of the material from the inner layers could be seen in the radioactive decay of nickel-56 to cobalt-56, and its subsequent decay to iron-56. Now, after more than 1000 hours of observation by Integral, high-energy X-rays from radioactive titanium-44 in supernova remnant 1987A have been detected for the first time. It is estimated that the total mass of titanium-44 produced just after the core collapse of SN1987A’s progenitor star amounted to 0.03% of the mass of our own Sun. This is close to the upper limit of theoretical predictions and nearly twice the amount seen in supernova remnant Cas A, the only other remnant where titanium-44 has been detected. It is thought both Cas A and SN1987A may be exceptional cases

Christoph Winkler, ESA’s Integral Project Scientist says “Future science with Integral might include the characterisation of high-energy radiation from a supernova explosion within our Milky Way, an event that is long overdue.”

Find out more about Integral here
and about Integral’s study of Supernova 1987A here