Hubble and Chandra discover a pair of supermassive black holes
Image of galaxy MCG-03-34-064 taken in visible light from the Hubble Space Telescope. Hubble’s sharp view shows three distinct bright spots embedded in a white oval at the center of the galaxy (enlarged in inset, top right). Two of these bright spots are sources of powerful X-rays, a telltale sign that they are supermassive black holes. Black holes shine brightly because they convert incoming matter into energy and race through space as active galactic nuclei.
They are about 300 light-years away. The third spot is a bright clump of gas. The blue stripe pointing to the 5 o’clock position could be a beam emitted from one of the black holes. A pair of black holes is formed by the merger of two galaxies that eventually collide. Image credit: NASA, ESA, Anna Trindade Falcão Like two wrestlers fighting, the next confirmed pair of supermassive black holes have been observed very close together. They are about 300 light years away and were discovered using NASA’s Hubble Space Telescope and Chandra X-ray Observatory. Buried deep within a pair of colliding galaxies, these black holes are driven by incoming gas and dust and shine brightly as active galactic nuclei (AGN).
This AGN pair is the closest one found in the local universe using multi-wavelength observations (visible light and X-rays). Dozens of “double” black holes have been found so far, but their spacing is usually much greater than the one found in the gas-rich galaxy MCG-03-34-64. Astronomers have used radio telescopes to observe pairs of binary black holes even closer than MCG-03-34-64, but not at other wavelengths. Such AGN binaries would have been more common in the early universe, when galaxy mergers were more common. The discovery offers a unique close-up look at a nearby example about 800 million light-years away. The discovery was a happy accident. Hubble’s high-resolution images show three light diffraction peaks inside the host galaxy, indicating a large concentration of glowing oxygen gas in a very small region.
“We didn’t expect to see something like this,” said Anna Trindade Falcão of the Harvard & Smithsonian Center for Astrophysics in Cambridge, Massachusetts. “This view showed us that this is not a common phenomenon in the nearby universe and that something different is going on in our galaxy.” Diffraction peaks are image artifacts that occur when light from a very small region of space bends around a telescope mirror.
Next, Falcao’s team used the Chandra Observatory to examine the same galaxy in X-rays to explore the issue even more deeply. “When we looked at MCG-03-34-64 in X-rays, we saw two separate sources of intense high-energy radiation that matched the bright spots of optical light observed by Hubble. We put these pieces together and concluded that we are probably looking at two closely packed supermassive black holes,” Falcao said. To support their interpretation, the researchers used archived radio data from the Karl G. Jansky Very Large Array near Socorro, New Mexico. The energetic black hole duo also emits powerful radio waves. “When we see bright light at optical, X-ray and radio wavelengths, we can rule out a lot of things and come to the conclusion that they can only be explained by black holes close to each other.
When we put all the pieces together, we get the image of an AGN duo,” Falcan said. The third bright source observed by Hubble is of unknown origin and more data is needed to understand it. It could be a gas shock caused by the energy of a jet of ultrafast plasma firing from one of the black holes, like a jet of water spurting from a garden hose onto a pile of sand. “Without Hubble’s incredible resolution, we wouldn’t have been able to see all these subtleties,” Falcao said. The two supermassive black holes once sat at the centers of their respective host galaxies. A galactic merger brought the black holes closer together. They will continue to spiral closer together until they finally merge, perhaps 100 million years from now, and shake the fabric of space-time as gravitational waves. The National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected gravitational waves from dozens of mergers between stellar-mass black holes.
However, the longer wavelengths produced by the merger of supermassive black holes are beyond the capabilities of LIGO. The next generation of gravitational wave detectors, called the Laser Interferometer Space Antenna (LISA) mission, will consist of three detectors in space millions of kilometers apart to detect these longer wavelength gravitational waves from space. ESA (European Space Agency) is leading the mission in collaboration with NASA and other participating agencies. The launch is planned for the mid-2030s.
Next, Falcao’s team used the Chandra Observatory to examine the same galaxy in X-rays to explore the issue even more deeply. “When we looked at MCG-03-34-64 in X-rays, we saw two separate sources of intense high-energy radiation that matched the bright spots of optical light observed by Hubble. We put these pieces together and concluded that we are probably looking at two closely packed supermassive black holes,” Falcao said. To support their interpretation, the researchers used archived radio data from the Karl G. Jansky Very Large Array near Socorro, New Mexico. The energetic black hole duo also emits powerful radio waves. “When we see bright light at optical, X-ray and radio wavelengths, we can rule out a lot of things and come to the conclusion that they can only be explained by black holes close to each other.
When we put all the pieces together, we get the image of an AGN duo,” Falco said. The third bright source observed by Hubble is of unknown origin and more data is needed to understand it. It could be a gas shock caused by the energy of a jet of ultrafast plasma firing from one of the black holes, like a jet of water spurting from a garden hose onto a pile of sand. “Without Hubble’s incredible resolution, we wouldn’t have been able to see all these subtleties,” Falcao said. The two supermassive black holes once sat at the centers of their respective host galaxies. A galactic merger brought the black holes closer together.
They spiraled closer and closer until they eventually merged, perhaps 100 million years from now, shaking the fabric of space-time as gravitational waves. The National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected gravitational waves from dozens of mergers between stellar-mass black holes. However, the longer wavelengths produced by the merger of supermassive black holes are beyond the capabilities of LIGO. The next generation of gravitational wave detectors, called the Laser Interferometer Space Antenna (LISA) mission, will consist of three detectors in space millions of kilometers apart to detect these longer wavelength gravitational waves from space. ESA (European Space Agency) is leading the mission in collaboration with NASA and other participating agencies. The launch is planned for the mid-2030s.
source: DOI: 10.3847/1538-4357/ad6b91