Black hole closer to Earth than thought

Astronomers have accurately measured the distance between Earth and a particular black hole for the first time. And wow, is it close.

The researchers determined that the black hole V404 Cygni is located 7,800 light-years from Earth — or just slightly more than half the distance that was previously assumed.

That puts it relatively nearby to Earth, where the distance to the center of the galaxy is about 26,000 light-years, and the nearest star beyond the sun is a mere 4.2 light-years away.
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The more accurate distance measurement will enable scientists to paint a better picture of how black holes evolve, the team says.

“For example, we hope to be able to answer the question as to whether there is a difference between black holes that evolve directly from the collapse of a star without a supernova and black holes that evolve via a supernova and a temporary intermediate star,” said study team member Peter Jonker of SRON Netherlands Institute for Space Research.

“We expect that the black holes in the last group can get a kick. Black holes formed in this way could then move through space faster.”

Jonker and his team measured the distance to V404 Cygni by measuring radio emissions from the black hole and its associated dying star.

The outermost layers of the star are being siphoned by the black hole. The swirling gas forms a hot plasma disk around the black hole before it disappears, and the process emits a lot of X-rays and radio waves.

Using an international system of radio telescopes called the High Sensitivity Array, the team measured the so-called parallax shift of the black hole system. This method involves measuring the annual movement in the sky of the black hole system as a consequence of Earth’s orbit around the sun.

The team says the previous overestimation of V404 Cygni’s distance was due to an underestimation of the absorption and diffraction of interstellar dust, which can give an error margin of about 50 percent. The error margin of the new measurement is less than 6 percent.