(ORDO NEWS) — A trail found in the gas surrounding a distant galaxy could be a smoking gun pointing to a runaway supermassive black hole.
Based on an analysis of light that has traveled over 7.5 billion years to reach the US, a team of astronomers has provided evidence of a colossal object ejected from its host galaxy 39 million years ago that is currently rushing through intergalactic space at a speed of 1,600 kilometers (994 miles) per second.
Although the black hole itself is invisible, there is no trace of it: shocks left in the rarefied intergalactic medium leave behind a trail of star formation in compressed gas.
The team’s work shows how we can identify dormant supermassive black holes ejected from their galaxies to move invisibly and unhindered through intergalactic space.
The study, led by astrophysicist Pieter van Dokkum of Yale University, has been completed. accepted in The Astrophysical Journal Letters and available on the arXiv preprint server.
The idea that a supermassive black hole could be ejected from its own galaxy isn’t really all that strange.
In fact, astronomers have already identified what they think may be several supermassive black holes ejected from the centers of their galaxies (although none have yet ventured into intergalactic space), and even one galaxy that appears to be , there is no supermassive black hole at all. p>
But all of these supermassive black holes had one thing in common: they are active, which means they are surrounded by a cloud of matter that falls into their gaping fatal maws. This process generates an insane amount of heat and light, making them much easier to spot.
But not all black holes are active. And the ones that go about their business between snacks, just go about their business, emit no light that we can detect, and are therefore virtually invisible to our technology.
However, something as massive as a supermassive black hole – millions and billions of times the mass of the Sun – could still leave traces that we can detect.
Van Dokkum and his colleagues suggested that the footprint of an ejected supermassive black hole could be found in the gas surrounding the galaxy, known as the circumgalactic medium.
The discovery was made during other investigations. The researchers used Hubble to study a much closer dwarf galaxy called RCP 28. It was in this image that they found something that could just be the trail of a runaway supermassive black hole.
The image showed a bright streak pointing straight at the center of the irregular galaxy. The researchers initially thought they were cosmic rays, but they showed up in both filters used for image processing.
So, in October 2022, they took additional pictures with the Keck Observatory to calculate the galaxy’s redshift and band. This gave them their size: the band is over 200,000 light-years long.
The analysis showed that the galaxy and the band have the same redshift, which means that they are probably related to each other, and the band and galaxy have the same color. The team has never seen anything like it.
Looking closely, they found that the band was not uniform in color or brightness. It also shows signs of strong ionization and shock regions.
Some of the ionization could be explained by the presence of very young, hot and massive stars; this is consistent with astrophysical impacts, which tend to compress the gas and cause its clumps to collapse under gravity to form young stars.
Bands of light emanating from the centers of galaxies are not unusual; usually these are astrophysical jets, powerful narrow streams of plasma moving at near-light speeds, launched from the polar regions of active supermassive black holes.
However, the band found by the team does not show any of the signs of an astrophysical jet.
It’s entirely possible, the team speculated, that the passage of the jet could have left a trail of star formation in its wake; but the streak in the images does not correspond to any recorded observed or simulated case of jet-induced star formation.
In fact, the observed band turns out to be the exact opposite of what astronomers would expect from a jet of gas; is strongest at the farthest point of the galaxy, where there is less material, and narrows over a greater distance rather than propagating like a jet.
The team believes the best explanation is a runaway supermassive black hole, perturbing and compressing the circumgalactic environment as it passes, leaving behind star formation.
You’re probably wondering what could throw a supermassive black hole out of its galaxy, and the answer is: another supermassive black hole.
Or two. According to the researchers’ scenario, two galaxies merged long ago; the supermassive black holes at the cores of these galaxies coalesced into a double supermassive black hole and remained so for some time.
Then a third galaxy appeared, and the supermassive black hole in it descended to the center of the recently merged trio of galaxies, resulting in a three-body interaction known as the Hills mechanism, which threw one of the black holes away at high speed.
Future observations at different wavelengths will help astronomers figure out if this is actually the case. Meanwhile, because the feature is so distinctive, other examples should be relatively easy to find, especially with more powerful instruments like the upcoming Nancy Roman Grace Infrared Space Telescope.
“We argue that this function is next to unmanaged SMBH based on the small number of papers written on the topic over the past fifty years,” the researchers write in their paper.
“This area could benefit from further theoretical work, especially as these works propose different mechanisms for trace formation. Fluid simulations that simulate shocks as well as taking into account gravitational effects can combine these initial studies into a self-consistent framework.”
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