Author: Lisa Grossman / Source: Science News for Students
Cosmic Seagull is a galaxy — a massive community of stars — some 11.3 billion light-years away.
This galaxy also hosts a mystery. Its outermost stars race way too fast to be propelled just by the gravity of the galaxy’s gas and stars. Instead, they move as if urged on by an invisible force. And that appears to point to the presence of dark matter, scientists now report.Most of the universe appears to be filled with dark matter, a mysterious, unseen material. Astronomers know it exists by the way its mass interacts — via gravity — with visible matter.
If the Cosmic Seagull is one such repository, it will be the most distant galaxy to be filled with dark matter.
Verónica Motta works at the University of Valparaíso in Chile. This astrophysicist and her colleagues shared their new findings August 8 at arXiv.org.
“In our nearby universe, you see these halos of dark matter around galaxies like ours,” she says. “So we should expect that in the past, that halo was there, too.” And because the light from distant galaxies is just reaching us from long, long ago, these new data point to the presence of dark matter back in those very ancient times.
Motta and her team used radio telescopes in Chile. They’re known as ALMA, which is short for the Atacama Large Millimeter/submillimeter Array. These telescopes have measured the speed of gas across the Cosmic Seagull’s visible disk, which spans out from the center across a distance of about 9,800 light-years. ALMA’s findings show that the galaxy’s stars speed up the farther they get from the galaxy’s center.
That’s a strange setup for most orbiting objects. When planets orbit a star, for instance, the most distant planets move the most slowly. But the Cosmic Seagull’s gas speeds can be explained if the galaxy’s far reaches are dominated…
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