X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI
Multiple images of a distant quasar are visible in this combined view from NASA’s Chandra X-ray Observatory and the Hubble Space Telescope.
Artist's impression of a spinning supermassive black hole with a surrounding accretion disk and relativistic jets.
How to measure the spin of a black hole: This chart illustrates the basic model for determining the spin rates of black holes. The three artist's concepts represent the different types of spin: retrograde rotation, where the disk of matter falling onto the hole, called an accretion disk, moves in the opposite direction of the black hole; no spin; and prograde rotation, where the disk spins in the same direction as the black hole.
Two models of black hole spin: Scientists measure the spin rates of supermassive black holes by spreading the X-ray light into different colors. The light comes from accretion disks that swirl around black holes, as shown in both of the artist's concepts. They use X-ray space telescopes to study these colors, and, in particular, look for a "fingerprint" of iron -- the peak shown in both graphs, or spectra -- to see how sharp it is. Prior to observations with NASA's Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency's XMM- Newton telescope, there were two competing models to explain why this peak might not appear to be sharp. The "rotation" model shown at top held that the iron feature was being spread out by distorting effects caused by the immense gravity of the black hole. If this model were correct, then the amount of distortion seen in the iron feature should reveal the spin rate of the black hole. The alternate model held that obscuring clouds lying near the black hole were making the iron line appear artificially distorted. If this model were correct, the data could not be used to measure black hole spin.
This chart depicts the electromagnetic spectrum, highlighting the X-ray portion. NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's XMM-Newton telescope complement each other by seeing different colors of X-ray light. XMM-Newton sees X-rays with energies between 0.1 and 10 kiloelectron volts (keV), the "red" part of the spectrum, while NuSTAR sees the highest-energy, or "bluest," X- ray light, with energies between 3 and 70 keV.
This image taken by the ultraviolet-light monitoring camera on the European Space Agency's (ESA's) XMM-Newton telescope shows the beautiful spiral arms of the galaxy NGC1365. Copious high-energy X-ray emission is emitted by the host galaxy, and by many background sources. The large regions observed by previous satellites contain so much of this background emission that the radiation from the central black hole is mixed and diluted into it. NuSTAR, NASA's newest X-ray observatory, is able to isolate the emission from the black hole, allowing a far more precise analysis of its properties.
What XMM-Newton saw: The solid lines show two theoretical models that explain the low-energy X-ray emission seen from the galaxy NGC 1365 by the European Space Agency's XMM-Newton. The red line explains the emission using a model where clouds of dust and gas partially block the X-ray light, and the green line represents a model in which the emission is reflected off the inner edge of the accretion disk, very close to the black hole. The blue circles show the measurements from XMM-Newton, which are explained equally well by both models.
Two X-ray observatories are better than one: NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has helped to show, for the first time, that the spin rates of black holes can be measured conclusively. It did this, together with the European Space Agency's XMM-Newton, by ruling out the possibility that obscuring clouds were partially blocking X-ray right coming from black holes. The solid lines show two theoretical models that explain low-energy X-ray emission seen previously from the spiral galaxy NGC 1365 by XMM-Newton. The red line explains the emission using a model where clouds of dust and gas partially block the X-ray light, and the green line represents a model in which the emission is reflected off the inner edge of the accretion disk, very close to the black hole. The blue circles show the latest measurements from XMM-Newton, and the yellow circles show the data from NuSTAR. While both models fit the XMM-Newton data equally well, only the disk reflection model fits the NuSTAR data.
Back when the universe was half its present age, supermassive black holes were feeding from a steady and plentiful diet of neighboring galaxies, the first measurement of a distant supermassive black hole’s spin shows.
Taking advantage of a naturally occurring zoom lens in space, astronomers analyzed X-rays streaming from near the mouth of a supermassive black hole powering a quasar about 6 billion light years from Earth.
“The ‘lens’ galaxy acts like a natural telescope, magnifying the light from the faraway quasar,” University of Michigan astronomer Rubens Reis explains in a paper published in this week’s Nature.
Analyzing four magnified images created by the lens galaxy -- an elliptical galaxy about 3 billion light years away -- Reis and colleagues found that the quasar’s black hole is spinning at half the speed of light.
The spin rate directly relates to how black holes feed and grow: The steadier the diet, the faster the spin, computer models show.
“If the mass accretion was more messy it would suggest that the black hole would have a lower spin,” astronomer Mark Reynolds, also with University of Michigan, told Discovery News.
“What we found in this system is that it’s spinning very rapidly,” Reynolds said, consuming mass equivalent to about one sun per year.
That suggests that the quasar, known as RX J1131-1231, is growing primarily by what is known as “coherent accretion” such as what might happen when two galaxies merge, producing lots of gas that can funnel down toward the black hole very efficiently, Reynolds said.
Until astronomers measure the spin rates of other and even more distant supermassive black holes they won’t know if RX J1131 is an odd bird or not.
“This is the first time that we’ve been able to push out to this type of distance by using the gravitational lensing effect. We hope ... to carry out similar studies on other (more distant) galaxies. Then we can begin to really start relating the black hole to the actual galaxy it’s in, how many mergers happened and things like that,” Reynolds said.
Spin rates may evolve over time, reflecting changes in evolution of galaxies.
“Different theories of galaxy evolution predict a different rate of mergers, and a different process of gas inflow into the center of galaxies,” Guido Risaliti, with the INAF Arcetri Astrophysical Observatory in Florence, Italy, wrote in an email to Discovery News.
“These processes, in turn, determine the final black hole spin. So knowing the distribution of supermassive black hole spins is a way to constrain the way they were formed, and so, ultimately, the way their host galaxies formed and evolved,” Risaliti wrote.
At some distance, the black holes’ spins might be even higher, approaching light speed, and then slow down to RX J1131’s spin rate.
“If we go back further, maybe they’ll all be maximally spinning because of more mergers and more things happening. Or maybe they’ll be less spinning. We can theoretically produce both scenarios at the moment,” Reynolds said.