![]() If the host galaxy ejected an SMBH, the galaxy should show signs of disruption. The researchers found that the three stars fall within the correct ranges of metallicity, age, and dust content to conform with a rogue SMBH that left its galaxy about 39 million years ago. This image from the work shows three knots in the tail that are likely recently formed stars. They’re also within the range of metallicities and dust content. When the researchers measured their properties, they found that the three knots are within the age range laid out by models. Theory and modelling show that the youngest stars formed in the wake should be younger than about 30 million years old. The researchers analyzed three of the knots in the linear feature and measured their ages and metallicity. In the wake, clouds of shocked gas can cool and form stars that look like knots in the trail. When an SMBH travels through ionized hydrogen in the CGM, it produces a shock front with a long wake trailing behind it. These images from the Hubble’s Advanced Camera for Surveys show the linear feature that may result from a rogue SMBH. In their paper, they report the serendipitous discovery of a linear feature in images from the Hubble’s Advanced Camera for Surveys that could be one of these wakes. “The interaction of a runaway supermassive black hole with the CGM can lead to the formation of a wake of shocked gas and young stars behind it,” the authors write. But without the luminosity from an AGN, the dimness makes identifying the hole and its stellar companions difficult from a great distance.Ī third way that astronomers could recognize a potential rogue SMBH is by the effect it has on the difuse gas in the circumgalactic medium (CGM) as it passes through it. When an SMBH is ejected, its massive gravitational power pulls some stars along with it. “For such objects,” the authors write, “the presence of an SMBH is not in doubt, but it can be difficult to determine whether they are ‘naked’ black holes or the nuclei of merging galaxies.”Īnother way is by the stellar mass that the rogue hole drags along with it. The easiest way is if the hole is actively absorbing material as an active galactic nucleus and can be identified by its luminosity. But they couldn’t conclude whether they saw an ongoing galaxy merger, a binary black hole system, or a gravitational-wave recoil event.Īstronomers recognize a couple of ways that they can identify a runaway SMBH. The authors noticed peculiar movement and velocity that indicated recent disruption. Astronomers identified one of the best candidates in 2021, about 230 million light-years away. If during that time, a third SMBH reaches the galactic center, then a three-body interaction can give one of the SMBHs a velocity boost, and it can be driven from the galaxy.īut despite their theoretical underpinnings, finding these rogue SMBHs is difficult. ![]() The binary SMBH can be very long-lived, surviving for as long as one billion years before merging. That leads to the formation of a binary SMBH at the center of the merger remnant. In their paper, the authors explain how an SMBH can be cast out of its host galaxy. But scientists think that in rare circumstances SMBHs can escape their galaxies. SMBHs are normally locked into place at the centers of galaxies, and that’s where they stay. If you’ve never heard of a runaway SMBH, you’re not alone.
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