Saturday, January 15, 2022

Black hole devoured a star decades ago and it was only discovered now

Traces of a black hole 's "meal" were identified in a dataset from the 1980s, thanks to two high school students. The object devoured a star, which was torn apart in a process known as a tidal disruption event, before crashing to the event horizon never to return.

 How black holes feed

A black hole's “lunch” is not a discrete process; on the contrary, it is a confusing and troubled event, which releases large amounts of radiation. When the star (or anything else unlucky) gets too close to the object, gravity pulls on it with violent force.

Despite this, the star still has a long way to go before reaching the event horizon — the critical point of a black hole from which nothing, not even light, can escape. Therefore, the star's matter is gradually stripped away, until it is spaghettied.

 This stellar mass "spaghetti" begins to spin at great speed around the black hole, producing a burst of light. And while astronomers have seen this phenomenon occur a few times, few of these cases have relied on radio observations.

Black hole meal found by teenagers

Young Ginevra Zaccagnini and Jackson Codd were reviewing data collected by the Very Large Array (VLA) in New Mexico and noticed that a bright signal seen in the mid-1990s had disappeared in 2017.

They left a note for scientists about the discovery, and so a team of astronomers began looking for other observations of the glow, cataloged as J1533+2727. They soon discovered that another radio telescope, at the Green Bank Observatory, Virginia, USA, had detected the same object before its sudden disappearance.

With the sum of the data, they realized that observations between 1986 and 1987 showed that the object appeared even brighter than those of the 1990s. Now, according to the team's calculation, the glow is now 500 times darker than it was at its brightest.

Looking further, they concluded that the glow was caused by a black hole feeding on a star, causing a tidal disruption event that resulted in a relativistic jet, detected by radio signals.

According to Vikram Ravi, an astronomer at the California Institute of Technology (Caltech) in Pasadena, "this is the first discovery of a candidate for a relativistic tidal disruption event in the relatively nearby universe." This could mean that this phenomenon may be more common than previously thought.

These glows emitted during black hole meals are great opportunities to study them. More than 100 such events were found in all. The paper describing the research has been accepted for publication in The Astrophysical Journal.

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