MessageToEagle.com - Astronomers at Case Western Reserve University have spotted a faint dwarf galaxy and
another possible young dwarf caught before it had a chance to form any stars.
These two celestial discoveries are located in the constellation Ursa Major (the Great Bear).
Within the faint trails of intergalactic traffic, the researchers also found more evidence pointing to two already
known dwarf galaxies as probable forces that pulled the pinwheel-shaped disk galaxy known as M101 out of shape.
M101 also known as is the dominant member in a group of 15 galaxies in Ursa Major. Most galaxies reside in such
small-group environments, which means the factors shaping M101 are likely the same shaping most galaxies throughout
the universe, the researchers say.
Click on image to enlarge
The Pinwheel Galaxy
This image of the Pinwheel Galaxy, also known as M101, combines data in the infrared, visible, ultraviolet and X-rays from four of NASA's space-based telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101's tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-ray vision, all at the same time.
The Pinwheel Galaxy is in the constellation of Ursa Major (also known as the Big Dipper). It is about 70 percent larger than our own Milky Way Galaxy, with a diameter of about 170,000 light years, and sits at a distance of 21 million light years from Earth. This means that the light we're seeing in this image left the Pinwheel Galaxy about 21 million years ago - many millions of years before humans ever walked the Earth.
Image Credits: X-ray: NASA/CXC/SAO; IR & UV: NASA/JPL-Caltech; Optical: NASA/STScI
"We created the deepest image ever taken of M101 and followed it up with the most sensitive survey of gas clouds
surrounding the galaxy," said Chris Mihos, an astronomy professor at Case Western Reserve University.
"Compared to what is seen in the Hubble Space Telescope image, the galaxy's disk is much larger and we can see
very large, faint plumes of stars and streamers of gas in its outskirts."
Perhaps most surprisingly, the researchers discovered two new clouds of hydrogen gas in the M101 group, more distant
and distinct from M101's own supply of gas.
The gas clouds, formally named G1425+5235 and G1355+5439, were nicknamed Skipper and Gilligan by the team, and
identified as new dwarf galaxies in the group, independent from M101 itself.
A follow-up analysis of images from the Sloan Digital Sky Survey showed a faint patch of starlight associated with
Skipper, confirming its status as a true dwarf galaxy with a population of both gas and stars.
"Gilligan could be a proto dwarf-galaxy, Mihos said, where the density of gas inside the cloud was too low for gravity
to squeeze the gas down and form stars.
"We'll follow up. There's a gas cloud but no stars yet. People have seen a few starless clouds before, but they've
always associated with gas from a larger galaxy.
This is different - it has nothing to link it to the other galaxies
in the group. It may be one of the first true protogalaxies ever discovered."
As galaxies move within galaxy groups, they may sideswipe one another or even run into each other head-on. These
intergalactic traffic jams leave behind telltale signatures in the galaxies' stars and gas.
In the faint light around M101, the researchers discovered such evidence of a sideswipe in the galaxy's past: a
distorted plume of starlight reaching far to the northeast of the galaxy, and a second plume extending to the east.
The shapes and colors of the plumes suggest that they formed when a small galaxy passed by M101, and its gravity
tugged stars and gas out from the bigger galaxy.
The northeast plume of the pinwheel is bluer than any other region of the galaxy, indicating it is made from younger stars.
"We think it was born about 250 million years ago. It has the right colors," Mihos said. "If the material in the
blue plume was pulled out of an interaction with another galaxy, the interaction was probably 250 million years ago.
"The eastern spur is redder, which is what you expect from an older set of stars. We think, unlike the blue plume
of new stars, the eastern spur formed when stars from the older, inner part of the disk were pulled out during