If you see a similar streak in one of your photos, you can take a few minutes to clean the lens. But the streak, in this case, was in an image taken by the Hubble Space Telescope, unaffected by the smudges that daily life leaves on hardware on Earth. So a team of researchers decided to find out what the long, thin smear might mean.
They aren’t sure yet, but the best explanation seems to be the wake left by a supermassive black hole that shot out of its host galaxy. Its release may have been the result of two more supermassive black holes, all of which were brought together by a galactic merger. If this is correct, it would be the first instance of this behavior that we have seen.
what is that?
Back in the days of film cameras, when months or even years could pass between taking a photograph and developing it, it wasn’t uncommon to take freshly made snapshots and wonder what you’d taken. A picture. You can hear echoes of those days in an astronomer’s description of a smear in one of Hubble’s images: “A nearly straight, thin line was immediately apparent upon visual assessment of data quality.”
At a closer look, the streak stretches out into a slightly odd-looking galaxy. “Having never encountered anything like this before in our own films or in the literature, we decided to add this feature to the surveillance program for the planned Keg. [telescope] Run.”
The streak (center in both images) appears to have originated in the upper right galaxy at two different wavelengths.
Van Tockum, et al. Eel.
Based on the redshift of light from the object, both it and the galaxy are roughly the same distance from Earth, suggesting that the two are related. Researchers estimate that the line is about 200,000 light-years long. When supermassive black holes at the center of galaxies emit long (and even longer) jets of material, those jets spread further out from the galaxy. In this case, the line was thin throughout its entire length.
Looking at the emission of stars in the streak shows that, in general, stars get younger as they move away from the galaxy. Taken together, this line began to form about 40 million years ago, and its tip is gradually moving away from the galaxy at a speed of about 1,600 kilometers per second.
Old theories
One possible explanation for that motion is that the galaxy ejected a supermassive black hole. This is inevitable because of two observations: almost all galaxies seem to have a supermassive black hole at their center, and most galaxies are bound by multiple mergers. As a result, the supermassive black holes of pre-merging galaxies will eventually run into each other. There are two ways this can lead to an exodus. For one thing, if these two supermassive black holes merge, the production of gravitational force is inconsistent, giving a directional kick to the post-merger product.
An alternative path to outflow occurs if one or more interstellar mergers take place in relatively rapid (astronomical terms) mergers where all their central black holes are unlikely to have merged yet. In these cases, three or more giants wrap around each other and gravitational interactions allow them to throw each other off.
