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Caught in the act: Astronomers may have observed massive black hole ‘awakening’ for first time

An artist’s impression of the galaxy SDSS1335+0728 lighting up by feeding on gas in its surroundings.
An artist’s impression of the galaxy SDSS1335+0728 lighting up by feeding on gas in its surroundings. Copyright ESO/M. Kornmesser
Copyright ESO/M. Kornmesser
By Lauren Chadwick
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Researchers hypothesise in a new study that they are observing a black hole become activated in a galaxy.


Astronomers say that changes to a galaxy they have been observing may be the result of a massive black hole awakening.

The galaxy SDSS1335+0728 began shining brighter in late 2019, prompting astronomers to track its changes.

Researchers said in a new study published in the journal Astronomy and Astrophysics on Tuesday that its changes may constitute the first time they have seen a black hole activating in real-time.

“Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” Paula Sánchez Sáez, an astronomer at the European Southern Observatory in Germany and the study’s lead author, said in a statement.

“Suddenly, its [core] starts showing dramatic changes in brightness, unlike any typical events we've seen before”.

“We noticed that the source is evolving; the properties of the sources are not constant. It's changing, in particular its energetic state. From this, we say the source is activating,” Sánchez Sáez added in an interview with Euronews Next.

“It's not clear what is producing this activation but we see the evolution, we see this activation”.

The researchers used different telescopes such as the European Southern Observatory’s Very Large Telescope in Chile to observe the source.

“We were fortunate enough to be the ones who were looking at the source at the right time,” she said.

Since December 2019, the galaxy has been radiating more ultraviolet and optical light and there was an increase in infrared luminosity three years later. It then started emitting x-rays in February.

The galaxy, which is located around 300 million light-years away in the constellation Virgo, had not shown variations over the previous two decades.

Chris Lintott, a professor of astrophysics at the University of Oxford who was not involved in the study, called it a “fascinating object”.

“Either it’s an extreme version of something we’ve seen before, or a process that we’ve never been able to watch happen,” Lintott told Euronews Next.

“We know that black holes at the centre of galaxies turn off and on, on timescales of tens of thousands of years, but it hadn’t occurred to me we’d be lucky enough to catch one in the act”.

Hypothesis to be confirmed

The astronomers said more research is needed to rule out other explanations for the activity.


One such explanation is that this is a tidal disruption event, a phenomenon where a star passes close to a black hole and is torn apart generating streaks of light.

The astronomers said this explanation was less favourable than that of a black hole awakening for several reasons.

“The variations that we see are not the classical ones we should observe in a normal tidal disruption event,” Sánchez Sáez said.

“Then, the source has been varying for a very long time. Normally these tidal disruption events last only a few thousands or hundreds of days,” she added.


The x-ray activity coming so late after the changes is another clue that this is not a classical tidal disruption event.

"We have an ongoing campaign to observe the source with other facilities, other instruments, to further understand what is going on. So with the data we have in hand, we cannot say which of these hypotheses is true, but we can say for sure that it's not a classical event. It's an event that we have never seen before,” she said.

Astronomers agree that as more telescopes provide new opportunities to observe the sky, there will be more data generated to help understand galaxies.

“There are hints that the Milky Way’s central black hole undergoes these cycles of activity, so we might be witnessing something that’s happened in our galaxy in the past, and which might happen again in the future,” Lintott said


“The discovery adds to the sense that this is a great time to be learning about black holes”.

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