Stupefied astronomers on Wednesday unveiled the first and only known galaxy without dark matter, the invisible and poorly-understood substance thought to make up a quarter of the Universe.
The discovery could revise or even upend theories of how galaxies are formed, they reported in the journal Nature.
“This is really bizarre,” said co-author Roberto Abraham, an astronomer at the University of Toronto.
“For a galaxy this size, it should have 30 times as much dark matter as regular matter,” he told AFP by phone. “What we found is that there is no dark matter at all.”
“That shouldn’t be possible,” he added.
There are 200 billion observable galaxies, perhaps more, astronomers estimate.
Some 65 million light-years from Earth, NGC1052-DF2 — “DF2” for short — is about the same size as our Milky Way, but has 100 to 1,000 times fewer stars.
Dark matter’s existence is inferred from the motion of objects affected by its gravitational pull.
“It is conventionally believed to be an integral part of all galaxies, the glue that holds them together and the underlying scaffolding on which they are built,” said co-author Allison Merritt from the Max Planck Institute for Astronomy, in Germany.
– One surprise after another –
So-called ordinary matter — including stars, gases, dust, planets and everything on them — accounts for only five percent of all content in the Universe.
Dark matter and dark energy comprise the rest, and scientists have yet to directly observe either.