Author: Emily Conover / Source: Science News
MISSING: Dark matter.
Mass: About 60 billion suns’ worth.
Location: The galaxy NGC1052–DF2, about 65 million light-years from Earth.
An unusual galaxy is surprisingly lacking in dark matter, scientists report March 28 in Nature.
In typical galaxies, normal matter is swamped by dark matter, an unidentified invisible substance that makes up most of the matter in the universe. The existence of dark matter explains the unexpectedly fast speeds at which stars swirl around galaxies, and how galaxies move within clusters.
But one galaxy, NGC1052–DF2, appears to have less dark matter than normal matter, or potentially none at all. Given its mass — it holds stars with about 200 million times the mass of the sun — it would be expected to have about 300 times as much dark matter as normal matter. That adds up to about 60 billion times the sun’s mass in missing dark matter.
Using observations from several telescopes, Yale University astronomer Pieter van Dokkum and colleagues studied 10 bright clumps of stars within the galaxy, known as globular clusters, and measured their velocities. The more mass there is in the galaxy, the faster the clusters should move around it. So if dark matter were present, the clusters should cruise at a relatively rapid clip. Instead, the clusters were moving slowly, indicating a dark matter–free zone.
In most galaxies, stars move faster than naïvely expected, which suggests dark matter lurks within them, providing an extra source of…
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