Hungry black hole regularly eats planet-sized chunks of star

New observations made with the Neil Gehrels Swift Observatory provide a "missing link" in our knowledge of black hole and star interactions.
Chris Young
An artist's impression of a black hole.
An artist's impression of a black hole.

Just_Super / iStock 

A Sun-like star in a galaxy near ours is slowly being eaten by a relatively small black hole.

Though it's small for a black hole, it is extremely active and devours the equivalent mass of three Earths every time the star passes close by, a press statement reveals.

The astronomers behind the discovery, from the University of Leicester, believe it provides a "missing link" in our knowledge of black holes interacting with and disrupting stars.

A black hole devouring a star

The new observations suggest there may be a whole host of undiscovered stars that are being gradually devoured by a nearby black hole.

The team behind the discovery was supported by the UK Space Agency and the UK Science and Technology Facilities Council (STFC). They published their findings in a new paper published in the journal Nature.

The astronomers discovered the star thanks to a bright X-ray flash emanating from the center of a nearby galaxy some 500 million light-years away called 2MASX J02301709+2836050.

The galaxy, called Swift J0230, was spotted using a new tool developed by the astronomers for the Neil Gehrels Swift Observatory. Instead of decaying away as expected, they found that it shone brightly for 7-10 days before suddenly going dark. Follow-up observations showed that this process repeated roughly every 25 days.

The behavior of Swift J0230's emissions had never been seen before.

Similar behavior has been observed in phenomena known as quasi-periodic eruptions and periodic nuclear transients. In both of these, a star gradually has material stripped away by a black hole. They are set apart, though, by the regularity of the emissions as well as the type of electromagnetic radiation that predominantly emanates from the eruption — either X-rays or optical light.

Swift J0230's behavior sits somewhere between the two, meaning it likely forms a "missing link" in our knowledge of black hole and star interactions.

Investigating a "missing link"

Using models of quasi-periodic eruptions and periodic nuclear transients as a guide, the astronomers found that the Swift J0230 event was likely caused by a star of a similar size to our Sun in an elliptical orbit around a low-mass black hole at its galaxy's center.

The black hole is estimated to be roughly 10,000 to 100,000 times the mass of our Sun, which is relatively small for one of the cosmic giants. As a point of reference, the supermassive black hole at the center of the Milky Way, Sagittarius A*, is estimated to have the equivalent of 4 million solar masses.

Every time the star makes a close approach, material equivalent to the mass of three Earths is devoured by the black hole. It is heated up to around 3 million degrees Fahrenheit (2 million degrees Celsius) as it's pulled into the black hole, releasing a massive amount of X-rays.

Dr. Rob Eyles-Ferris, one of the University of Leicester astronomers on the study, said that "in most of the systems we've seen in the past the star is completely destroyed. Swift J0230 is an exciting addition to the class of partially-disrupted stars as it shows us that the two classes of these objects already found are really connected, with our new system giving us the missing link."

Another one of the astronomers who worked on the data analysis for the study, Dr. Kim Page, said, "Given that we found Swift J0230 within a few months of enabling our new transient-hunting tool, we expect that there are a lot more objects like this out there, waiting to be uncovered."

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