A streak of light may not be a black hole fleeing its galaxy after all. In February, astronomer Pieter van Dokkum of Yale University and colleagues reported spotting a line of stars near a compact galaxy in Hubble Space Telescope images. The researchers’ analysis suggested that three galaxies had interacted and merged, kicking a supermassive black hole out of its host galaxy (SN: 3/10/23).
The black hole then traveled through a nearby gas cloud, the scenario goes, triggering the formation of stars in a line that points toward the home galaxy and revealing the black hole’s madcap escape.
But other researchers have been skeptical of this interpretation, with some suggesting that the scenario is too complex to explain the linear feature. In the new study, “we decided to explore what we thought was the most simple explanation,” says astronomer Ignacio Trujillo of the Instituto de Astrofísica de Canarias in Tenerife, Spain.
He was inspired by a data plot in the original study, which compared the velocities of the stars in the linear feature with their positions, a comparison known as a velocity curve. To him, it looked like a spiral galaxy’s plot of its pinwheel rotation, where the stars in the galactic disk all move at nearly the same speed, no matter if they appeared to travel toward or away from Earth (SN: 8/17/21).
That, combined with van Dokkum and colleagues’ estimate of the feature’s mass — roughly 100 million suns, which was surprisingly large for a simple line of stars — implied that the object is actually a spiral galaxy viewed on its edge, Trujillo says.
So he and his colleagues compared characteristics of the linear feature with those of a well-studied spiral galaxy called IC 5249, which astronomers know we see edge on from Earth.
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