Free Astronomy Magazine September-October 2022

49 SEPTEMBER-OCTOBER 2022 ASTRO PUBLISHING T he Triangulum galaxy, or M33, is shown here in far-infrared and radio wavelengths of light. Some of the hydrogen gas (red) that traces the edge of the Triangulum’s disc was pulled in from intergalactic space, and some was torn away from galaxies that merged with Triangulum far in the past. The image is composed of data from the European Space Agency (ESA) Herschel mission, supplemented with data from ESA’s retired Planck observatory and two retired NASA missions: the Infrared Astronomy Survey and Cosmic Background Explorer, as well as the Very Large Array, Green Bank Telescope, and IRAM radio telescope. [ESA, NASA, NASA-JPL, Caltech, Christopher Clark (STScI), E. Koch (University of Alberta), C. Druard (University of Bordeaux)] Triangulum galaxies. All four are within 3 million light-years of Earth. In the images, red indicates hydro- gen gas, the most common element in the universe. The image of the Large Magellanic Cloud shows a red tail coming off the bottom left of the galaxy that was likely created when it collided with the Small Magellanic Cloud about 100 million years ago. Bub- bles of empty space indicate regions where stars have recently formed, because intense winds from the newborn stars blow away the sur- rounding dust and gas. The green light around the edges of those bubbles indicates the presence of cold dust that has piled up as a re- sult of those winds. Warmer dust, shown in blue, indicates where stars are forming or other processes have heated the dust. Many heavy elements in nature – like carbon, oxygen, and iron – can get stuck to dust grains, and the presence of different elements changes the way dust absorbs starlight. This in turn affects the view astronomers get of events like star formation. In the densest dust clouds, almost all the heavy ele- ments can get locked up in dust grains, which increases the dust-to- gas ratio. But in less dense regions, the destructive radiation from new- born stars or shockwaves from ex- ploding stars will smash the dust grains and return some of those locked-up heavy elements back into the gas, changing the ratio once again. Scientists who study interstel- lar space and star formation want to better understand this ongoing cycle. The Herschel images show that the dust-to-gas ratio can vary within a single galaxy by up to a fac- tor of 20, far more than previously estimated. “These improved Herschel images show us that the dust ‘ecosystems’ in these galaxies are very dynamic,” said Christopher Clark, an as- tronomer at the Space Science Tele- scope Institute in Baltimore, Mary- land, who led the work to create the new images. These results were featured in a press conference at the summer meeting of the Ameri- can Astronomical Society. !