Have you ever burped（打嗝） after a meal？Recently，scientists from Harvard University found a black hole that"burped out"the star it had"eaten".
Back in 2018，a small star was seen to be"eaten"by a black hole that is 665 million light years away from Earth. Three years later，the same black hole became active again. This time（喷出）materials of the star at half the speed of light. This event is called AT2018 hyz.
"This caught us completely by surprise —no one has ever seen anything like this before，"said Yvette Cendes，a researcher on this.
A black hole's eating of a star is called a tidal disruption event （TDE）. Although TDEs happened a few times before，but the ejecting has only taken place at the same time as the eating，the speed of the materials ejected from the black hole is also unusual，as most TDE outflows travel at 10% the speed of light rather than half of it.
The team thought about the possible reasons behind the event. They first turned to the density theory（密度理论）. If the density is very high around the black hole，the materials might be drawn out，causing a"burp". Another explanation was that the other TDEs happened in directions that could not be seen from Earth. So other black holes' gravity drew the materials out.
However，scientists have not yet found the true reason. But they say they will work hard on it.
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