In December 2019, astronomers were stunned when the core of a relatively quiet galaxy 300 million light-years away abruptly lit up like a Christmas tree and shone brighter than we’ve ever seen it.
A giant black hole that accelerated and started slurping material from the space around it is the best explanation for such a faint galaxy suddenly beaming with light. Other events, such as exploding stars, can cause a distant galaxy to brighten, but these events usually fade over time.
SDSS1335+0728, as the galaxy is known, didn’t do the typical thing. In fact, it has become even brighter and still shines in optical, infrared and ultraviolet light to this day. More recently, in February of this year, X-rays were even started to be emitted.
‘The most tangible option to explain this phenomenon is to see how the… [core] of the Milky Way is beginning to show activity,” says astronomer Lorena Hernández García of the Millennium Institute of Astrophysics (MAS) and the University of Valparaíso in Chile.
“If so, this would be the first time we’ve seen the activation of a massive black hole in real time.”
Black holes don’t just sit around in space all the time. They can only access material within their gravitational range. When there is nothing around, they remain relatively quiet or calm. For example, the supermassive black hole at the center of the Milky Way is not classified as active because it is only minimally feeding.
An active supermassive black hole, on the other hand, causes the space around it to light up. Of course, the black hole itself doesn’t shine; but when there is enough matter around it to sustain a feeding frenzy, the forces involved, such as friction and gravity, cause the material to heat up so extremely that it glows with light as it swirls inexorably toward the black hole.
Galaxies with varying levels of activity in their cores have been observed across the vast expanse of space-time, yielding models that suggest that guzzling large amounts of material is one of the mechanisms by which supermassive black holes grow to such colossal sizes.
There is also evidence that supermassive black holes can change their activity levels. For example, the Milky Way has giant bubbles extending above and below the galactic plane from previous activity at its center. Other galaxies have similar characteristics.
But it is very special to see the transition from a quiet phase to an active one.
We’ve seen black holes suddenly flare up with light before; This is usually what’s known as a tidal disruption, where a passing star or other blob of matter becomes ensnared by a lurking black hole, creating a flash of light as it is torn apart and devoured.
An extensive analysis of the change in light produced by SDSS1335+0728 and its 1.5 million solar-mass black hole shows that a tidal disruption is not the most likely culprit; Such events are also usually short-lived.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard writing; encrypted media; gyroscope; photo within photo; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>
“In the case of SDSS1335+0728,” says astronomer Claudio Ricci of Diego Portales University in Chile, “we were able to observe the awakening of the massive black hole. [which] suddenly began to feast on the gas available in the vicinity, and became very bright.”
Astronomers have recently seen other examples of what could be a supermassive black hole entering an active phase, but further observations are needed to determine whether the increase in brightness continues.
This means that SDSS1335+0728 could be a blueprint for what such a transition would look like. Because we don’t know what causes a supermassive black hole to turn back on, studying the galaxy can help astronomers develop models.
This in turn could reveal the likelihood of this happening elsewhere, including here in our own galaxy, the Milky Way.
However, it is possible that the brightening of SDSS1335+0728 is due to a very peculiar form of tidal disruption. Astronomers will continue to watch it closely to confirm what it does and what this behavior could mean for our understanding of the universe.
The research was published in Astronomy and astrophysics.