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.
One of the most enduring mysteries behind the dynamics of supermassive black holes, and their impacts on galactic evolution, has been uncovered by an international team of astrophysicists.
Using the ESO’s Very Large Telescope (VLT), located in the Atacama desert in northern Chile, researchers from the UK, Netherlands and the US have studied the core of a nearby galaxy in great detail. The galaxy, called IC5063, has a very active central supermassive black hole that appears to drive rapid outflows of molecular hydrogen from the galaxy. IC5063 is known as a Seyfert galaxy, a very active type of galaxy with a bright core.
Many active galactic nuclei have been observed with these outflow features and, as molecular hydrogen is key to the formation of stars, astronomers have realized that its ejection impacts star formation and, therefore, galactic evolution. As the majority of galaxies are thought to contain supermassive behemoths in their cores, the activity of these black holes (that have masses of tens to hundreds of millions of suns) can control the quantity of gas supplied to star forming regions.
But how do black holes accelerate this cold hydrogen gas to hundreds of thousands of miles per hour? Until now, that has been hard to fathom.
From the VLT observations, astronomers headed by Clive Tadhunter of the University of Sheffield have found that the outflow is driven by jets of relativistic electrons, which are being ejected from the dynamic environment just outside the black hole’s event horizon. Whenever the highly energetic electrons blast through clouds of molecular hydrogen, the gas is transported out of the galaxy, starving it of star-forming material.
“Much of the gas in the outflows is in the form of molecular hydrogen, which is fragile in the sense that it is destroyed at relatively low energies,” said Tadhunter, who collaborated with researchers from the Netherlands Institute of Radio Astronomy and the Center for Astrophysics, Harvard. “It is extraordinary that the molecular gas can survive being accelerated by jets of electrons moving at close to the speed of light.”
The research has been published in the journal Nature.
Interestingly, this study provides a small hint as to what our galaxy can expect when it collides with the neighboring Andromeda galaxy in around 5 billion years time. The merging of the two galaxies will inject matter into the central supermassive black holes, kick-starting powerful jets. When this occurs, would-be star-forming molecular gas will be ejected also, possibly stymieing star formation and changing the evolutionary outcome of our Milky Way.