Spiral
98. in Serpens
This new NASA/ESA Hubble Space Telescope image shows a beautiful spiral galaxy
known as PGC 54493, located in the constellation of Serpens (The Serpent). This galaxy
is part of a galaxy cluster that has been studied by astronomers exploring an intriguing
phenomenon known as weak gravitational lensing.
This effect, caused by the uneven distribution of matter (including dark matter)
throughout the Universe, has been explored via surveys such as the Hubble Medium
Deep Survey. Dark matter is one of the great mysteries in cosmology. It behaves very
differently from ordinary matter as it does not emit or absorb light or other forms of
electromagnetic energy — hence the term “dark”.
Even though we cannot observe dark matter directly, we know it exists. One
prominent piece of evidence for the existence of this mysterious matter is known as
the “galaxy rotation problem”. Galaxies rotate at such speeds and in such a way that
ordinary matter alone — the stuff we see — would not be able to hold them together.
The amount of mass that is “missing” visibly is dark matter, which is thought to make
up some 27% of the total contents of the Universe, with dark energy and normal
matter making up the rest. PGC 55493 has been studied in connection with an effect
known as cosmic shearing. This is a weak gravitational lensing effect that creates tiny
distortions in images of distant galaxies.
Credit: ESA/Hubble & NASA
“Hubble brought the Universe into our backyard. Or rather,
it expanded our backyards to enclose the Universe itself.
It did that with images so intellectually, visually, and even
spiritually fulfilling that most don’t even need captions.”
— Neil deGrasse Tyson
Director of Hayden Planetarium
American Museum of Natural History
New York, New York