(ORDO NEWS) — When we see images of galaxies outside the Milky Way, we usually see the light from their stars first. But stars are far from the only ingredient that makes up a galaxy. Think of the stars as bits of vegetables in a galactic soup.
Then the soup in which they swim is the intergalactic medium – not empty space, but filled with often rarefied, sometimes dense clouds of dust and gas drifting between stars.
Because stars are much brighter, dust usually comes second; but the dust from which stars are born, into which stars return, can tell us a lot about the structure and activity within the galaxy.
Four new images have now been released showing the distribution of dust in the four closest galaxies to the Milky Way: the Large and Small Magellanic Clouds, dwarf galaxies orbiting our own; the Andromeda Galaxy, a large spiral galaxy 2.5 million light-years away; and the Triangulum Galaxy, a spiral galaxy 2.73 million light-years away.
A galaxy without dust and gas as we know them would not exist. Stars form when a dense knot of material in a cold cloud of molecular gas collapses under the force of gravity, taking in material from the surrounding cloud.
When this star dies, it ejects its outer material back into space around it, along with the new, heavier elements it has fused during its lifetime.
New stars being born include the dust of dead stars, making each successive generation of stars a little different. We are indeed all made of stellar matter even stars.
But the dust is unevenly distributed. Stellar winds, galactic winds, and the effects of gravity can push and mold interstellar dust into complex shapes filled with cavities. Mapping the structures and the composition of the elements within them is an important tool for understanding the formation of… well… almost everything.
The new images, presented at the 240th meeting of the American Astronomical Society, were taken by the European Space Agency’s Herschel Space Observatory between 2009 and 2013. Prior to the launch of Webb, who had yet to provide his first scientific images, Herschel was the largest infrared telescope ever launched.
Like Webb, its ultra-low operating temperature meant that Herschel could look into the far infrared, displaying some of the coldest and dustiest objects in space, down to about -270 degrees Celsius (-454 degrees Fahrenheit). This includes cold clouds where stars are born and dust in interstellar space.
However, it was less capable of detecting more diffuse dust and gas. To fill in the gaps, a team of astronomers led by Christopher Clark of the Space Telescope Science Institute used data from three other decommissioned telescopes: ESA’s Planck and NASA’s Infrared Astronomy Satellite (IRAS) and the Cosmic Background Explorer (COBE).
The results show complex interactions within the dust. Hydrogen gas is displayed in red; it’s the most abundant element in the universe, so there’s quite a lot of it.
The cavities in the dust, where newborn stars have blown it away with strong winds, appear as empty areas surrounded by a green glow indicating cold dust. The blue areas represent warmer dust heated by stars or other processes.
The images also reveal new information about the complex interactions that take place in interstellar dust, the researchers say.
Heavy elements such as oxygen, carbon and iron can often stick to dust particles; in very dense clouds, most of the elements are associated with dust, which increases the ratio of dust to gas. This can affect how light is absorbed and re-emitted by the dust.
However, violent processes such as star birth or supernovae can release radiation that destroys dust, releasing heavy elements back into gaseous clouds. This shifts the ratio of dust to gas back towards gas.
Herschel’s images show that relationships in the galaxy can vary by up to 20 times. This is much more than astronomers thought, important information that could help scientists better understand this cycle.
And they are just incredibly beautiful. Who knew Andromeda’s soup could be such a dazzling rainbow color.
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