When we look at images of galaxies outside of the Milky Way, we're generally gazing at the light from their stars. However, stars are far from the only component of a galaxy. Consider stars to be the veggies in a cosmic soup.
The intergalactic medium, therefore, is the soup in which they float — not empty space, but clouds of dust and gas that flow between the stars, often fragile, sometimes thick. Because stars are so much brighter, dust takes a back seat; nonetheless, dust, from which stars are produced and to which stars return, may reveal a lot about a galaxy's structure and activity.
The dust distribution in four of the closest galaxies to the Milky Way has been revealed in four new images: 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.
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| The Large Magellanic Cloud |
Galaxies as we know them would not exist without dust and gas. Stars are formed when a compact knot of material collapses under gravity in a cold cloud of molecular gas, absorbing material from the surrounding cloud. When a star dies, it ejects its outer material into the surrounding space, together with the new, heavier elements it fused during its lifespan.
As new stars are created, the dust from previous generations is incorporated, resulting in somewhat distinct generations of stars. All of us, even the stars, are formed of star material.
The dust, however, is not evenly dispersed. Interstellar dust may be pushed and sculpted into complicated structures filled with voids by star winds, galactic winds, and gravity's influence. Understanding the creation of... well... pretty much anything begins with mapping the structures and the composition of the materials within them.
The new photographs, which were shown during the American Astronomical Society's 240th conference, were taken by the European Space Agency's Herschel Space Observatory between 2009 and 2013. Herschel was the world's biggest infrared telescope until the launch of Webb, which has yet to produce its first science photographs.
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| The Small Magellanic Cloud |
Herschel, like Webb, had an ultracold working temperature that allowed it to image some of the coldest and dustiest objects in space at temperatures as low as -270 degrees Celsius (-454 degrees Fahrenheit). This encompasses the dust in interstellar space as well as the frigid clouds in which stars are formed.
However, it struggled to identify more dispersed dust and gas. A team of astronomers led by Christopher Clark of the Space Telescope Science Institute utilized data from three other decommissioned observatories to fill in the gaps: the European Space Agency's Planck, NASA's Infrared Astronomical Satellite (IRAS), and the Cosmic Background Explorer (COBE).
The findings indicate intricate interplays in the dust. The most prevalent element in the Universe, hydrogen gas, shows in red; there is a lot of it. Cavities in the dust appear as empty patches, encircled by a green light that signifies cold dust, where nascent stars have driven it away with their powerful winds. Warmer dust, heated by stars or other sources, is represented by blue zones.
According to the researchers, the photos also disclose fresh information about the intricate interactions that occur in interstellar dust. Heavy elements like oxygen, carbon, and iron may commonly cling to dust grains; in the densest clouds, the majority of elements are bonded to dust, resulting in a higher dust-to-gas ratio. This can have an impact on how dust absorbs and re-emits light.
Violent activities like star formation or supernovae, on the other hand, can generate radiation that breaks up the dust, releasing the heavy elements back into gaseous clouds. This causes the dust-to-gas ratio to shift back to gas.
The Herschel photos show that in a galaxy, ratios can vary by up to a factor of 20. That's a lot more than astronomers expected, and it's crucial knowledge that might help scientists better comprehend the cycle.
They're also stunningly beautiful. Who knew Andromeda soup could come in such a spectrum of colors...
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