Astronomers have discovered 854 previously hidden 'ultra dark' galaxies,
that may be filled with mysterious dark matter, in a region known as
the Coma Cluster.
The discovery surpasses the last year's discovery of
47 mysterious dark galaxies by more than 800 and suggests that galaxy
clusters are the key environment for the evolution of such galaxies.
"The
finding suggests that these galaxies appear very diffuse and are very
likely enveloped by something very massive," said Jin Koda, principal
investigator of the study and Associate Professor in the Department of
Physics and Astronomy at Stony Brook University in New York, US.
The ultra-dark galaxies are similar in size to the Milky Way, but have only 1/1,000 of stars that our galaxy does.
The
stellar population within such fluffy extended galaxies is subject to
rapid disruption due to a strong tidal force detected within the
cluster.
"We believe that something invisible must be protecting
the fragile star systems of these galaxies, something with a high mass,"
said Koda.
"That 'something' is very likely an excessive amount
of dark matter," Koda said. The component of visible matter, such as
stars, is calculated to contribute only one percent or less to the total
mass of each galaxy. The rest - dark matter - accounts for more than 99
percent.
The Subaru Telescope, located at the Mauna Kea
Observatory on Hawaii, showed that these dark galaxies contain old
stellar populations and shows a spatial distribution similar to those of
other brighter galaxies in the Coma Cluster.
It suggests that
there has been a long-lived population of galaxies within the cluster
and the amount of visible matter they contain, less than one percent, is
extremely low compared to the average fraction within the universe.
These
galaxies are dark because they have lost gas needed to create new stars
during, or after, their largely unknown formation process billions of
years ago. From their preferential presence within the cluster, it's
likely that the cluster environment played a key role in the loss of
gas, which affects star formation within the galaxy.
Several loss
mechanisms are possible, including ram-pressure stripping by
intra-cluster gas, gravitational interactions with other galaxies within
the cluster, and gas outflows due to simultaneous supernova explosions
triggered by the ram pressure or gravitational encounters.
The
Coma Cluster is a large cluster of galaxies that contains over 1,000
identified galaxies. Along with the Leo Cluster, it is one of the two
major clusters comprising the Coma Supercluster.
Dark matter is a
hypothetical kind of matter that cannot be seen with telescopes but
would account for most of the matter in the universe.
The finding was published in the Astrophysical Journal Letters.
Coma Cluster’s Distance Closer Than Predicted, Amplifying Hubble Tension Crisis24 January 2025
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