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The galaxy NGC 1277, just a quarter the size of our own Milky Way, hosts a black hole 4,000 times larger than the one at the Milky Way's centre. A report in Nature shows it has a mass some 17 billion times that of our Sun. The surprise finding is hard to reconcile with existing models of black hole growth, which hold that they evolve in tandem with host galaxies. Getting to grips with just how large black holes are is a tricky business - after all, since they swallow light in their vicinities, they cannot be seen.
Instead, astronomers measure the black holes' "sphere of influence" - the gravitational effects they have on surrounding gas and stars. In the Milky Way, it is possible to observe individual stars as they orbit Sagittarius A, our own local black hole, to guess its mass. But for the 100 or so far more distant black holes whose masses have been estimated, astronomers have made average measurements of associated stars' speeds - their "velocity dispersion". On a hunt for the Universe's largest black holes, astronomers using the Hobby-Eberly Telescope in the US state of Texas undertook a survey that brought in a haul of nearly 900 host galaxies.
'Big jigsaw'
But Remco van den Bosch, then at the University of Texas at Austin, and his colleagues were surprised to find that some of the largest black holes were to be found in small galaxies. Among them was NGC 1277, 220 million light years away in the constellation Perseus, which happens to appear also in a high-resolution Hubble Space Telescope image, helping the researchers to refine their computer models. "We make a model of the galaxy and compute all the possible stellar orbits," Dr Van den Bosch, who is now at the Max Planck Institute for Astronomy in Germany, explained to BBC News. "Like a big jigsaw, we try to put those orbits together to reproduce that galaxy so it has the same stellar velocities we measure. " What the team found was that the NGC 1277 black hole was enormous - as large as our Solar System, and comprising some 14% of the entire galaxy's mass.
"The only way to you can actually make those high dispersions in the centre is by having that really big black hole, there's really no other way around it," Dr Van den Bosch said. What is more, the team have five other small-galaxy candidates that, with the help of more data, could disprove the rule that big black holes only happen in big galaxies. But NGC 1277 is stranger still, and could help advance our theories of how black holes evolve in the first place. "This galaxy seems to be very old," Dr Van den Bosch said. "So somehow this black hole grew very quickly a long time ago, but since then that galaxy has been sitting there not forming any new stars or anything else. "We're trying to figure out how this happens, and we don't have an answer for that yet. But that's why it's cool."
BBC News - Giant black hole in tiny galaxy confounds astronomers
Researchers have proposed a new means for getting a measure of just how massive supermassive black holes are. They are known to exist at the centres of most galaxies, but a puzzle remains as to how they affect galaxy evolution. The approach, published in Nature, infers a black hole's mass from the speed of molecules swirling around it. It could help weigh hundreds of nearby black holes. Its first use suggests a black hole in the NGC4526 galaxy has a mass 450 million times that of our Sun. Only in a few dozen cases have the masses of supermassive black holes been estimated. Because they cannot be seen directly, astronomers have relied on guessing how large they are based on the motion of objects circling them. Most estimates have come from gathering up starlight. This can be done by calculating how much faster the stars nearer the black hole are moving relative to those farther away.
However, that is an average measure, and the "random motions" of stars - not necessarily in the same direction as the swirling mass - blurs the measurement. The movement of electrically charged gas can be tracked in the same way, with slightly less blurring due to random motion. But these approaches remain painstaking and limited to only the nearest galaxies' black holes. The new work focuses instead on cold, dense masses of gas that have markedly less random motion, and which emit their radiation in the microwave part of the electromagnetic spectrum. That allows the use of telescopes and arrays with far better resolution. Timothy Davis of the European Southern Observatory and colleagues made use of the Carma array of telescopes in California, US, looking specifically for the radiation coming from molecules of carbon monoxide. They focused their efforts on NGC4526, mapping out the movements of the molecules at various distances from the galaxy's central black hole.
Using their new technique, they estimated the black hole has a mass of some 900 billion trillion trillion tonnes - on the heavy side even in the supermassive stakes. Estimates such as this may help finally unravel the interplay between black holes and the galaxies that host them. "Galaxies and black holes seem to be related to each other; there's this relation between the mass of the black hole and properties of the galaxy," explained Dr Davis. "That's rather weird, because these black holes are tiny compared to galaxies; they don't weigh that much, and they're physically small - less than the size of our Solar System in a galaxy that's billions of times bigger," he told BBC News. "What we'd really like to understand is how these two components interact; why they care about each other at all. To do that, we need to be able to measure their masses, and compare them in all sorts of different galaxies. That will allow us to start answering these questions."
The estimate was based on data gathered at the 23-telescope Carma array in California
With the new method in hand, Dr Davis said that next-generation telescopes tuned to these microwave frequencies - such as the Alma telescope in Chile - would be able to easily acquire the masses of hundreds of black holes. "The observations we present in the paper took over 100 hours on the Carma telescope," he said. "We estimate that with Alma you'll be able to reproduce those observation in 10 minutes. It's a real game-changer."
BBC News - Supermassive black hole weighed using new scale
Measurements undertaken with two space-based X-ray telescopes imaged the black hole at the centre of galaxy NGC 1365. The spin measurement, published in Nature, gives precious clues as to how the black hole grew and achieved supermassive status. That growth influences the evolution of galaxies, so this simple number stands to teach scientists a great deal. Black holes are notoriously difficult to study, since so much in astronomy depends on the detection of light - and beyond a certain distance, even that cannot escape.
Black holes are known to draw in material - gas and even stars - and stretching the very fabric of space-time at their edges. As matter goes in and gathers into what is called an accretion disk, it heats up and emits X-rays. Previous attempts to quantify black holes' spins have attempted to analyse these X-rays - accounting for the violent processes within that can stretch and distort the X-rays' energies. Those studies have until now focused on a fairly low-energy X-ray range. But those lower-energy X-rays can be further distorted by layers of gas between the black hole and the Earth, and previous spin observations have been contentious.
The Nuclear Spectroscopic Telescope Array (Nustar) was launched in mid-2012
In a spin
Now Guido Risaliti of the Harvard-Smithsonian Center for Astrophysics and colleagues have looked at markedly higher energies - less subject to absorption in those gas layers - using Europe's XMM-Newton telescope and the recently launched Nustar telescope. Nustar is unprecedented in its ability to focus in on distant parts of the cosmos in these high-energy X-rays. The results suggest a black hole more than 3 million km across, whose outermost edge is moving at a speed near that of light. But as Dr Risaliti explained, "the black hole's spin is a memory, a record, of the past history of the galaxy as a whole". Had the black hole grown in a series of small "feeds" of gas or stars from random directions, its spin would be low. The results instead suggest that the black hole grew in one or a series of large absorptions of matter, taking on the momentum in one or a few events.
And as Christopher Reynolds of the University of Maryland explains in an accompanying article in Nature, understanding the evolution of such supermassive black holes at galaxies' centres is crucial to our understanding of how galaxies themselves grow. "The energy released by a growing supermassive black hole can be so powerful that it disrupts the normal growth of the host galaxy," Prof Reynolds wrote. "In extreme cases, (it) can terminate all subsequent growth of the galaxy." However, the measurement is that of just one galaxy, and Prof Reynolds notes that even more advanced X-ray observatories will be needed to unravel the riddle with so few clues.
BBC News - First glimpse of a black hole's spin
The black hole lies at the centre of the Sculptor galaxy, a so-called starburst galaxy where stars are being born at a prodigious rate. But the X-ray light corresponding to a black hole's snack has dimmed markedly. The find, to appear in Astrophysical Journal, has mystified astronomers because star formation and black hole activity tend to go hand-in-hand. The Sculptor galaxy - also known as NGC 253 - hosts a central black hole with a mass some five million times that of our Sun - a quarter again as plump as the black hole at the centre of our own Milky Way galaxy.
In 2003, researchers using the Chandra space telescope caught sight of the X-rays that correspond to matter spiralling down into the black hole and heating up to millions of degrees. But as of mid-2012, the X-ray sky has a new observer: a space telescope called the Nuclear Spectroscopic Telescope Array or Nustar, already a successful black-hole hunter.
Optical and X-ray telescope views show plenty of new stars - but no feeding black hole
Nustar can spot even higher-energy X-rays than Chandra, and in late 2012, both telescopes were trained on NGC 253 - with the surprise finding that the X-ray emission seems to have stopped. "Black holes feed off surrounding accretion disks of material. When they run out of this fuel, they go dormant," said Ann Hornschemeier of Nasa's Goddard Space Flight Center, a co-author on the new study. "NGC 253 is somewhat unusual because the giant black hole is asleep in the midst of tremendous star-forming activity all around it."
The subtle interplay between black hole activity and the birth rate of new stars remains somewhat mysterious, but Bret Lehmer of Nasa's Goddard Space Flight Center, lead author on the paper, said that the Sculptor galaxy could shed new light on these dark galactic corners. "Periodic observations with both Chandra and Nustar should tell us unambiguously if the black hole wakes up again. If this happens in the next few years, we hope to be watching," he said.
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What happened to the debris it ingested, where did it go?...
Black hole caught napping after meal
12 June 2013 > A black hole 11 million light-years away has gone dormant, a decade after being spotted consuming cosmic debris.
The black hole lies at the centre of the Sculptor galaxy, a so-called starburst galaxy where stars are being born at a prodigious rate. But the X-ray light corresponding to a black hole's snack has dimmed markedly. The find, to appear in Astrophysical Journal, has mystified astronomers because star formation and black hole activity tend to go hand-in-hand. The Sculptor galaxy - also known as NGC 253 - hosts a central black hole with a mass some five million times that of our Sun - a quarter again as plump as the black hole at the centre of our own Milky Way galaxy.
In 2003, researchers using the Chandra space telescope caught sight of the X-rays that correspond to matter spiralling down into the black hole and heating up to millions of degrees. But as of mid-2012, the X-ray sky has a new observer: a space telescope called the Nuclear Spectroscopic Telescope Array or Nustar, already a successful black-hole hunter.
Optical and X-ray telescope views show plenty of new stars - but no feeding black hole
Nustar can spot even higher-energy X-rays than Chandra, and in late 2012, both telescopes were trained on NGC 253 - with the surprise finding that the X-ray emission seems to have stopped. "Black holes feed off surrounding accretion disks of material. When they run out of this fuel, they go dormant," said Ann Hornschemeier of Nasa's Goddard Space Flight Center, a co-author on the new study. "NGC 253 is somewhat unusual because the giant black hole is asleep in the midst of tremendous star-forming activity all around it."
The subtle interplay between black hole activity and the birth rate of new stars remains somewhat mysterious, but Bret Lehmer of Nasa's Goddard Space Flight Center, lead author on the paper, said that the Sculptor galaxy could shed new light on these dark galactic corners. "Periodic observations with both Chandra and Nustar should tell us unambiguously if the black hole wakes up again. If this happens in the next few years, we hope to be watching," he said.
Source
