Space

Supermassive black hole found to rotate near speed of light

Emission of fluorescence x-rays from iron atoms in the accretion disk of a supermassive black hole (Photo: NASA/JPL)
Emission of fluorescence x-rays from iron atoms in the accretion disk of a supermassive black hole (Photo: NASA/JPL)
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Emission of fluorescence x-rays from iron atoms in the accretion disk of a supermassive black hole (Photo: NASA/JPL)
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Emission of fluorescence x-rays from iron atoms in the accretion disk of a supermassive black hole (Photo: NASA/JPL)
Illustration of two approaches to explain observed x-ray broadening near an SBH – relativistic effects, and obscuration (Photo: NASA/JPL)
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Illustration of two approaches to explain observed x-ray broadening near an SBH – relativistic effects, and obscuration (Photo: NASA/JPL)
Spectrum changes depending on rotation of accretion disk (Photo: NASA/JPL)
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Spectrum changes depending on rotation of accretion disk (Photo: NASA/JPL)
NASA/JPL NuSTAR x-ray space telescope (Photo: NASA/JPL)
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NASA/JPL NuSTAR x-ray space telescope (Photo: NASA/JPL)
Artist's conception of an accretion disk around a supermassive black hole (Photo: NASA/JPL)
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Artist's conception of an accretion disk around a supermassive black hole (Photo: NASA/JPL)
Combined x-ray data from XMM-Newton and NuSTAR showing agreement with relativistic distortions from rapidly rotating SBH in NGC 1635 (Photo: NASA/JPL)
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Combined x-ray data from XMM-Newton and NuSTAR showing agreement with relativistic distortions from rapidly rotating SBH in NGC 1635 (Photo: NASA/JPL)

The rotation of a supermassive black hole (SBH) has been definitively measured for the first time by combining x-ray data obtained by the x-ray space telescopes XMM-Newton (soft x-rays) and NuSTAR (hard x-rays). The SBH at the center of a galaxy called NGC 1365 was found to be spinning at 84 percent of the maximum speed allowed by general relativity – or roughly speaking, the edge of the black hole is rotating at 84 percent of the speed of light.

Supermassive black holes are the largest known objects of their type, with masses millions or billions times the mass of our sun. It is believed that all most, if not all, galaxies contain an SBH at their center. SBHs are surrounded by an accretion disk of dust and gas, which represents matter falling into the black hole.

Most black holes spin, or more precisely, have angular momentum. As the galaxy is rotating about the SBH, the infalling matter brings angular momentum along with it. This angular momentum causes the spacetime surrounding the SBH to rotate, an effect called frame dragging. There is a maximum rate at which the spacetime can rotate – the linear speed of the frame dragging must be less than the speed of light, roughly speaking. It is not clear, however, what we should expect for the angular momentum of an SBH – we don't even know how they are formed, or why there is one at the center of galaxies.

Artist's conception of an accretion disk around a supermassive black hole (Photo: NASA/JPL)
Artist's conception of an accretion disk around a supermassive black hole (Photo: NASA/JPL)

Fortunately, scientists have developed a way of measuring the spin of an SBH. Near the SBH, the accretion disk is very hot (as seen above), and emits a large amount of x-rays. In particular, x-rays associated with excited iron atoms are easily seen. Their appearance, however, is odd. They are broadened over a wide range of energy, and their distribution holds clues as to the rate at which the SBH is spinning.

The iron x-rays are generated by fluorescence near the inner edge of the accretion disk. This means that the source of the iron x-rays is moving rapidly around the SBH, so the spectrum of the iron x-rays is spread out by the general relativistic equivalent of the Doppler effect.

Illustration of two approaches to explain observed x-ray broadening near an SBH – relativistic effects, and obscuration (Photo: NASA/JPL)
Illustration of two approaches to explain observed x-ray broadening near an SBH – relativistic effects, and obscuration (Photo: NASA/JPL)

The structural features of the iron x-ray spectrum now allows us to determine the rotational speed of the SBH. The intensity varies with x-ray energy between the limits of five and fifty kiloelectron volts (keV). X-ray observations using space telescopes that, like the ESA's XXM-Newton, are sensitive to soft x-rays (1-10 keV) revealed the broadening, but this limited data agreed with several explanations, so that the rotation of the SBH could not be determined from those measurements.

NASA/JPL NuSTAR x-ray space telescope (Photo: NASA/JPL)
NASA/JPL NuSTAR x-ray space telescope (Photo: NASA/JPL)

NASA's NuSTAR (Nuclear Spectroscopic Telescope ARray) is an x-ray space telescope launched into orbit in mid-2012. Being sensitive to energies from six to 79 keV, it images objects that generate x-rays at larger energies than do the earlier generation of x-ray space telescopes.

Combined x-ray data from XMM-Newton and NuSTAR showing agreement with relativistic distortions from rapidly rotating SBH in NGC 1635 (Photo: NASA/JPL)
Combined x-ray data from XMM-Newton and NuSTAR showing agreement with relativistic distortions from rapidly rotating SBH in NGC 1635 (Photo: NASA/JPL)

An international team used NuSTAR to take a spectrum of the hard x-rays associated with the fluorescence of the iron atoms. This new information showed unambiguously that the alternate models to explain the line broadening were false, and allowed the astronomers to fix the angular momentum of the NGC 1365 SBH to be at least 84 percent of the maximum possible value, which is the speed of light.

The astronomers say the findings will help to shed light on how black holes and galaxies evolve.

Source: NASA/JPL

14 comments
Mel Tisdale
Old Mother Nature is capable of some pretty extraordinary feats. We go against her will at our peril.
Sara Seifert
We live at our own peril. The Catch-22 of all time! LOL
Kwazai
Amazing how similar the quantum affects are to the Higgs-Boson assumptions (scattering probabilities). I wonder how similar the math is after changes to the assumptions for the mass effects. Higgs-Boson Collider effects have included very small, very short lived black holes (from what I've read).
Phil
I am not sure how black holes work, but anything spinning that fast would be like a disc, and razor sharp thin, I presume, and as we go towards the centre of the disc, it would be going slower, kind of like a wheel. Eventually at dead centre we would be turning, but not at a near light speed, just at the number revolutions per second?. So if we have this mass that is enormously heavy, at least to us, spinning near the speed of light, perhaps the centre of the mass would gradually move to the outer edge and leave a hole in the middle? Or perhaps the slowly moving high density mass at the centre would gradually move at right angles to the spin and start looking like a spinning top? Either way I think the artists depiction in this article is incorrect. It is not a black ball. Another thing, I presume that the mass of the black hole spinning disc is fluid, and therefore it is not physically like a solid wheel, so most of its mass must be at the edge? And as it spins faster and approaches the speed of light, wouldn't all of the mass gradually migrate out to the spinning edge, and wouldn't it be approaching infinite mass? And would it not spread it self out so thin that it would go further and further out until it consumes the whole galaxy? Or am I talking complete rubbish?
Craig Jennings
You said it yourself Phil, if you're at the centre, you're not spinning around quickly... so why would you spin to the outside? But that's not the important part. Think if a black hole were a cone here on earth. You drop a marble in, it runs to the bottom. You flick that marble in... it spins around and goes to the bottom. You flick that marble in at 84% the speed of light and you die, but if you didn't and the cone was a super tough road cone version it'd still end up at the bottom of the cone eventually. Remember... light doesn't get out... that gradient is a bitch. If everything flattened out like that we'd be in trouble, aggregation would be a little tricky. Gravity seems to be a blackholes thing, spinning is just a byproduct from the momentum from the attracted mass. We're probably all talking complete rubbish. A name for something which has the mass of billions of our suns... arrogant little monkeys the lot of us! :P Cool article!!!!!!!!!!!!!!!
DarthTanner
@Phil You have the idea a bit wrong. A black hole is like the ultimate vacuum, sucking things in. Think about a comet headed towards the sun, when it gets nearer to the sun it actually ends up going around the sun faster. The mass of a black hole is so large that light is unable to escape its pull. So your idea is right, but backwards.
Dave987
Sorry Phil, but the salient feature of a black hole is that for anything (whether it be photons or bits of black hole) to escape from inside the event horizon, they would require a velocity greater than the speed of light, so the black hole insn't going to expand and wipe out the galaxy!
Phil
I would like to thank everyone who took the time to comment back to me about how black holes work, I guess I have more reading to do! Cheers
Tom Howell
Mother nature's way of attempting to keep space clean? SBVC - super big vacuum cleaner?
steve02
To be moving at such speed ... speed of light, I think we should look at using this concept for the interstellar ship.
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