Image courtesy of ESO and Digitized Sky Survey 2 O.
Joel Kontinen
Some stars
are slow but others are fast. Now scientist have discovered the fastest star at
the centre of our galaxy.
Stefan Gillessen at the Max Planck Institute
for Extraterrestrial Physics in Germany and his colleagues found S301 using the
Very Large Telescope in Chile.
At its
closest approach, S301 is only about 1.8 billion kilometres from Sagittarius A*, the supermassive black hole at the centre of our galaxy. That’s just 12
times the distance between Earth and the sun, 10 times closer to Sagittarius A*
than the previous record-holder. “If you were living on a planet
around this star, the size of the black hole at the closest approach would
appear similar to the full moon from Earth – it would be absolutely stunning,”
says Gillessen.
“Earth does
this as well, and we can measure with satellites around Earth that there is a
very, very slight frame dragging from Earth’s rotation,” says Tuan Do at
the University of California, Los Angeles, who wasn’t involved in the research.
“This is doing the same thing, just with much different objects.”
Measuring
Earth’s spin is relatively easy, but a black hole’s spin is much harder to
determine because of its lack of a visible surface. The most precise way to
measure it would be by measuring frame dragging, and S301 is the first star
close enough to feel that effect.
“We drop a
leaf in the wind and see how the air is moving by measuring that leaf,” says
Gillessen. “A star is just the perfect leaf to drop to see the movement of
space-time.”
Actually
measuring the spin of Sagittarius A* using this method will probably take
around a decade, he says, but that may speed up if we find more stars like it.
“With one
star, it would take a while, but it would still be the best constraint on spin
that we’ve ever had by far,” says Ziri Younsi at University College London. “If you can
find another star that’s even closer, that’s better still. If you can find a
population of these stars, then you’re in business.”
But when we
finally do measure the spin of a black hole, it will be a crucial piece of
the cosmic jigsaw. It will not only help us understand how black holes have contributed to the evolution of the
universe, but will also provide a probe into the behaviour of gravity in
extreme environments, which has proved extremely difficult to study.
By Leah Crane 2026
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