Seeds of Monster Black Holes Were Surprisingly Big
Credit: ESO/M. Kornmesser
This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Image released June 20, 2013.
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.
The gigantic black holes that lurk at the hearts of galaxies were apparently born big.
The central black holes in dwarf galaxies — the "seeds" that grow into the monsters at the core of the Milky Way and other large galaxies — are probably surprisingly weighty, containing 1,000 to 10,000 times the mass of our sun, a new study reports.
The finding goes against one popular theory of supermassive black hole evolution, suggesting that galaxy mergers aren't necessary to create these behemoths, which can harbor billions of times more mass than the sun. [The Strangest Black Holes in the Universe]
"We still don't know how the monstrous black holes that reside in galaxy centers formed," lead author Shobita Satyapal, of George Mason University in Virginia, said in a statement. "But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early universe, before galaxies collided with other galaxies."
It's also possible that supermassive black holes grow primarily by gobbling up gas and dust, getting bigger relatively sedately along with their host galaxies, researchers said.
Satyapal and her colleagues analyzed observations of dwarf galaxies made by NASA's Wide-field Infrared Survey Explorer spacecraft, or WISE.
Dwarf galaxies have changed relatively little over time, and they resemble the types of galaxies that existed when the universe was young. So they're a good place to look for nascent supermassive black holes, researchers said.
WISE's all-sky survey picked out hundreds of dwarf galaxies, which appear to sport strikingly large black holes.
"Our findings suggest the original seeds of supermassive black holes are quite massive themselves," Satyapal said.
While the results are intriguing, follow-up study will be necessary to fully flesh them out, outside researchers said.
"Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack," astronomer Daniel Stern, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. Stern was not part of the study team.
WISE launched to Earth orbit in December 2009 on a 10-month mission to scan the entire sky in infrared light. It was shut down in February 2011, then reactivated in September 2013 with a new mission and a new name. Now called NEOWISE, the spacecraft is hunting for potentially dangerous asteroids, some of which could be promising targets for human exploration.
The new study was published in the March issue of The Astrophysical Journal.
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