* Astronomy

Blobrana · L

RE: HE0450-2958

Blobrana · L

HE0450-2958

Blobrana · L

Black Hole Caught Zapping Galaxy into Existence?

Which come first, the supermassive black holes that frantically devour matter or the enormous galaxies where they reside? A brand new scenario has emerged from a recent set of outstanding observations of a black hole without a home: black holes may be "building" their own host galaxy. This could be the long-sought missing link to understanding why the masses of black holes are larger in galaxies that contain more stars.

"The 'chicken and egg' question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today. Our study suggests that supermassive black holes can trigger the formation of stars, thus 'building' their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars" - lead author David Elbaz.

To reach such an extraordinary conclusion, the team of astronomers conducted extensive observations of a peculiar object, the nearby quasar HE0450-2958, which is the only one for which a host galaxy has not yet been detected. HE0450-2958 is located some 5 billion light-years away.

Read more

Blobrana · L

QSO HE0450-2958

Blobrana · L

RE: HE0450-2958

Blobrana · L

BlackHole
A collision between two galaxies may have led them to spit out a colossal black hole that’s still soaring through space, some astronomers have calculated.

If correct, the proposal would be the first evidence of a possibility, astrophysicists have theorized for years: a black hole’s expulsion from a galaxy.
Indirectly, it could also shed light on how some black holes became as big as they are—a longstanding puzzle that’s also entangled with the question of how galaxies formed.
A team of researchers describe the results in a paper to appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society, a research journal.
They claim an enigmatic object known as HE0450-2958, estimated to weigh as much as 400 million suns or more, may be the expelled black hole.

HE0450-2958 is designated as a quasar, one of a class of objects that has puzzled scientists for decades. Quasars shine stupendous amounts of light across huge distances, some from practically the edge of the known universe.
What they are is uncertain, but most scientists think they’re probably gargantuan black holes, objects consisting of vast amounts of matter crammed into a small space. Black holes have overpowering gravity that drags in anything nearby with such force that the sucked-in objects are shredded and heated, so that they radiate intense light.
Quasars are thought to sit at the centres of big galaxies. This is because most galaxies appear to harbour giant black holes at their cores, so this seems a logical place for a quasar. Quasars would shine so brightly because they’re eating the stars and other material plentifully available in the surrounding galaxy.

But HE0450-2958, estimated to lie more than 3 billion light-years away from us—a light-year is the distance light travels in a year—seems to have no large home galaxy. This has puzzled astronomers, because without this, it should have little to “eat” and thus shouldn’t be shining brightly.
The new research suggests HE0450-2958 is an expelled black hole that still enjoys a quasar-like diet, possibly because it dragged enough material along with itself during its ejection to do so.
The scenario fits with calculations suggesting such events should occasionally happen when two galaxies collide, the researchers noted.

Moreover, the merged galaxy that they identify as black hole’s former home is still nearby, a paltry 20,000 light years away. It’s shining strongly with what seems to be widespread star formation, an expected by-product of a merger.

"Each of the merging galaxies is expected to have contained at least one supermassive black hole" - Martin G. Haehnelt of the University of Cambridge in Cambridge, U.K, and colleagues in the paper.

The expelled hole would have been one of those monoliths. Haehnelt’s team calculated it has been speeding away from the home galaxies at some 300 kilometres per second on average, more than 100 times faster than the fastest aircraft.
The crash is thought to have occurred some 100 million years before the hole got to where we see it now.
Two existing theories explain how colliding galaxies might eject a giant black hole.
In one, two galaxies merge, one of which already contains two huge black holes thanks to a previous merger. The new merger puts three supermassive black holes close together. They start orbiting each other because of their gravity.
But three objects don’t orbit each other very easily. They do a complex dance that often leads to violent rejection for the smallest one, due to what astronomers call a “gravitational slingshot” from the other two.
In the other scenario, each merging galaxy has one supermassive black hole. These eventually crash together, emitting a blast of a peculiar form of radiation called gravitational waves, whose existence Einstein postulated. If this burst is stronger in one direction than in others, it should kick the hole the opposite way, as a gun recoils when it fires.
Either way, the results could shed light on the formation of black holes—and through that the evolution of galaxies.

Astrophysicists have trouble explaining how black holes got as big as they apparently did, very early in cosmic history. Two competing views suggest the holes either grew through repeated mergers, or by sucking in whatever was around them.
There’s a related problem in explaining how galaxies became so big, so early in the history of the universe. Since black holes and galaxies seem to be intimately linked, astrophysicists suspect the problems are related.
If the speeding quasar results from a black hole merger, it ironically suggests mergers weren’t a major way for black holes to grow, as the merger would shoot them into deep space—away from other black holes with which to merge.
Independently of Haehnelt’s group, other researchers have also been studying whether HE0450-2958 is a rejected black hole. Some agree it is. Others don’t.

David Merritt of the Rochester Institute of Technology in Rochester, N.Y., posted a paper on the Internet Friday saying the object is surrounded by too much gas to be an ejected black hole. It would have lost that gas during the ejection, he wrote.
But if it is a tossed-out hole, Haehnelt claimed, its exile might not be permanent: the far-reaching gravity of the merged galaxy may well be strong enough to eventually drag it home.

Source

Blobrana · L

The quasar on the left, HE0450-2958 (in the centre, distance about 5 billion light-years) does not have a massive host galaxy. The quasar HE1239-2426 to the right (at a distance of 1.5 million light-years), has a normal host galaxy which displays large spiral arms.
Although HE1239-2426 is much closer than HE0450-2958, the host galaxy of the latter would still be perfectly visible if it was as bright as that of HE1239-2426.

Expand (173kb, 1662 x 881)

The lack of a prominent host galaxy around a very bright quasar (HE0450-2958) suggests a rare case of a collision between a seemingly normal spiral galaxy and an exotic object harbouring a very massive black hole.

Also seen in the image to the left (above the quasar) is a strongly disturbed galaxy, showing all the signs of a recent collision. The VLT observations show it to be forming stars at a frantic rate. A foreground star is seen below the quasar.
The two images have been scaled to exhibit the same linear scale.
The images were taken with Hubble's Advanced Camera for Surveys in October 2004.

Blobrana · L

Astronomers have detected a massive black hole but can find no traces of the surrounding galaxy that should be feeding it.
Using the Hubble Space Telescope and the European Southern Observatory's Very Large Telescope in Chile, an international team examined 20 quasars and found that quasar HE0450-2958, a quasar located some 5 billion light-years away, did not appear to have a galaxy surrounding it.

At the centre of most large galaxies are extremely dense black holes that have masses hundreds of millions times that of the Sun.
Called quasars, these massive black holes are the most radiant objects in the universe, outshining even the brightest galaxies. While the black holes themselves are invisible, friction and heat from the swirling matter they swallow emit huge amounts of radiation that can be detected by radio telescopes.

Quasars must feed off the galaxies they live within to maintain their brightness. That is why the discovery of a galaxy-less quasar is surprising.

The quasar on the left (the central bright spot) appears to have no host galaxy, while the one on the right has a normal host galaxy with spiral arms (Image: NASA/ESA/ESO/Frédéric Courbin/Pierre Magain)
Position(2000): RA = 04:52:30.05 Dec = -29:53:35.1

“We must therefore conclude that, contrary to our expectations, this bright quasar is not surrounded by a massive galaxy” - Pierre Magain, astronomer from the University of Liege in Belgium and lead author of a new study documenting the finding.

Quasars are relatively small compared to the galaxies they outshine. They are only about the size of our solar system, but they can emit up to 100 times as much radiation as an entire galaxy.
However, because quasars can be 100 times brighter than their host galaxies, it is very difficult to spot the fainter objects. There is still a possibility that a galaxy may surround quasar HE0450-2958.

"We cannot conclude anything general from one case" - Pierre Magain.

In the late 1990s, mathematical “deconvolution” algorithms were developed that could be applied to images after they were transmitted to Earth and which were capable of separating light from quasar’s from that of their host galaxies. Since then, astronomers have shown that nearly all quasars are encircled by a host galaxy.
In this case, the researchers detected a cloud of ionised gas about 2,500 light years in size near HE0450-2958. Dubbed "the blob," the researchers believe this gas cloud is what’s feeding the black hole, allowing it to become a quasar. The researchers estimate that the quasar is siphoning off about one Sun’s worth of mass each year from the blob.

Adding to the mystery is the detection of a deeply distorted galaxy located 50,000 light years away from the quasar. This so-called “companion” galaxy appears to be an extremely active stellar nursery, birthing new stars at a rapid rate, and it is also brighter in the infra-red spectrum than most galaxies.

The existence of these two unusual objects near the quasar could have been associated with a massive collision 100 million years ago. The black hole could have captured the blob of gas from the neighbouring galaxy as it was slowly passing by, resulting in the ignition of the quasar. But that fails to explain what happened to the quasar’s original host galaxy.

One of Magain's favoured explanations for the appearance of the lone quasar is that it may actually be surrounded by a halo of dark matter.
Such a collision would have stirred up dust and gas and enhanced the formation of stars, said Gèraldine Letawe, a member of the research team also from University of Liege in Belgium. Heat from the seething young stars, combined with dust and gas warmed up by the collision might be responsible for the galaxy’s intense infra-red glow.

To explain the strange cosmic setup they’ve discovered, the researchers have come up with various hypotheses, all of them equally strange:

It’s possible that the quasar does have an encircling galaxy, but that it is too small and too faint to be detected. If a host galaxy does exist, then it would have to be either six times fainter than typical host galaxies or have a radius smaller than 300 light years. Most quasar host galaxies range between 6,000 and 50,000 light years across.

The quasar may not have always been galaxy-less, but the collision with the companion galaxy may have somehow caused the quasar’s galaxy to disappear completely. The researchers note, however, that it is "hard to imagine how the complete disruption of a galaxy could happen."
The blob could be gas stolen by a slow-moving black hole as it travelled through the disc of a spiral galaxy.

Perhaps the most intriguing theory is that the quasar is encircled by a galaxy made up almost entirely of dark matter, a theoretical substance which is thought to make up 25 percent of the matter in the universe but which cannot be directly detected using current technologies.

Computer simulations of galaxy collisions might be able to determine if the first two options are plausible.

It may be possible to verify whether the galaxy is made up of dark matter by scanning the space around the quasar for evidence of gravity lensing, a phenomenon whereby a massive celestial object warps the fabric of space-time so much that light from distant objects is bent around it.

Another way to test for the presence of dark matter energy may be to look for gases that appear to be moving as if drawn by the gravity of some unseen object.

The discovery is documented in the September 15 issue of the journal Nature.

source