Young Stars in the Outskirts of Galaxies Finally Have an Explanation

Star formation is well understood when it happens in the populous centers of galaxies. From our vantage point on Earth, within the Milky Way, we see it happening all around us. But when newborn stars are birthed in the empty outskirts of galactic space, it requires a new kind of explanation. At the 243rd meeting of the American Astronomical Association yesterday, astronomers announced that they have observed, for the first time, the unique molecular clouds that give rise to star formation near the remote edges of galaxies.

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Could Life Exist in Molecular Clouds?

This image from the APEX telescope, of part of the Taurus Molecular Cloud, shows a sinuous filament of cosmic dust more than ten light-years long. Could life exist in molecular clouds like this one? Credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin.

Our search for life beyond Earth is still in its infancy. We’re focused on Mars and, to a lesser extent, ocean moons like Jupiter’s Europa and Saturn’s Enceladus. Should we extend our search to cover more unlikely places like molecular clouds?

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Speedrunning Star Formation in the Cygnus X Region

Cygnus X is a massive star formation region about 4600 light-years away. New research shows star formation occurring very rapidly. Image Credit: By NASA - http://www.nasa.gov/mission_pages/spitzer/multimedia/pia15253.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=19475200

Stars are born in molecular clouds, massive clouds of hydrogen that can contain millions of stellar masses of material. But how do molecular clouds form? There are different theories and models of that process, but the cloud formation is difficult to observe.

A new study is making some headway, and showing how the process occurs more rapidly than thought.

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One of Life’s Building Blocks can Form in Space

A new kind of chemical reaction can explain how peptides can form on the icy layers of cosmic dust grains. Those peptides could have been transported to the early Earth by meteorites, asteroids or comets. Image Credit: © S. Krasnokutski / MPIA Graphics Department

Peptides are one of the smallest biomolecules and are one of life’s critical building blocks. New research shows that they could form on the surfaces of icy grains in space. This discovery lends credence to the idea that meteoroids, asteroids, or comets could have given life on Earth a kick start by crashing into the planet and delivering biological building blocks.

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Astronomers Find a Giant Cavity in Space, Hollowed out by an Ancient Supernova

A cavity of empty space was likely caused by a supernova. Credit: Alyssa Goodman/Center for Astrophysics | Harvard & Smithsonian

Star formation is a topic astronomers are still trying to fully understand. We know, for example, that stars don’t form individually, but rather are born within vast interstellar molecular clouds. These stellar nurseries contain gas dense enough for gravity to trigger the formation of stars. In spiral galaxies, these molecular clouds are most commonly found within spiral arms, which is why stars are most often born in spiral arms.

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This is a Simulation of the Interstellar Medium Flowing Like Smoke Throughout the Milky Way

The figure shows a section through the cube of the turbulence simulation. The colors show the density contrast relative to the mean density of the gas. Its turbulent structure is clearly recognizable. Image Credit: Federrath et al, 2021.

How do stars form?

We know they form from massive structures called molecular clouds, which themselves form from the Interstellar Medium (ISM). But how and why do certain types of stars form? Why, in some situations, does a star like our Sun form, versus a red dwarf or a blue giant?

That’s one of the central questions in astronomy. It’s also a very complex one.

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We’re Made of Starstuff. Especially From Extremely Massive Stars

An illustration of a protoplanetary disk. The solar system formed from such a disk. Astronomers suggest this birthplace was protected by a larger filament of molecular gas and dust early in history. Credit: NASA/JPL-Caltech/T. Pyle (SSC)
An illustration of a protoplanetary disk. The solar system formed from such a disk. Astronomers suggest this birthplace was protected by a larger filament of molecular gas and dust early in history. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

A new study shows how massive young stars create the kind of organic molecules that are necessary for life.

A team of researchers used an airborne observatory to examine the inner regions around two massive young stars. Along with water, they found things like ammonia and methane. These molecules are swirling around in a disk of material that surrounds the young stars.

That material is the same stuff that planets form from, and the study presents some new insights into how the stuff of life becomes incorporated into planets.

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The Corona Australis Molecular Cloud. Normally this Looks Like a Dark Blob in the Sky. But in Infrared, it Looks Like This.

A composite image of the Corona Australis molecular cloud from the ESA's Herschel and Planck Space Observatories. Image Credit: ESA/Herschel/Planck; J. D. Soler, MPIA

The Corona Australis is a constellation in the southern hemisphere. It’s name literally means “southern crown.” One of its features is the Corona Australis molecular cloud, home to a star-forming region containing young stars and proto-stars. It’s one of the closest star-forming regions to us, only about 430 light years away.

The ESA has given us a new composite image of the cloud with data from the Herschel Space Observatory and the Planck Space Observatory.

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Deep Astrophoto of LDN 673: The Place Where Stars are Born

LDN 673, a molecular cloud complex in the constellation Aquila. Credit and copyright: Callum Hayton.

What a stunning view of this dark region of space! This image, by astrophotographer Callum Hayton shows LDN 673, a molecular cloud complex that lies in the constellation Aquila. This region is massive — around 67 trillion kilometers (42 trillion miles across), and it is between 300-600 light years from Earth. Observers in the northern hemisphere can find this region in the summer skies near the bright star Altair and the Summer Triangle.

Because the cloud lies on the galactic plane, the dark dust is back-lit by millions of stars in the Milky Way galaxy. This dusty cloud likely contains enough raw material to form hundreds of thousands of stars. Hayton explained on Flickr how the dust gets “eroded” away by stellar formation:

“When some of these clouds reach a certain mass they begin to collapse and fragment creating protostars,” Hayton wrote. “As the temperature and pressure at the centre of the protostar rises, sometimes it becomes so great that nuclear fusion begins and a star is born. In this image you can see where at least two young stars have eroded the dust around them and are now above the clouds casting light down on to the dust below.”

Gorgeous!

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Mapping Molecular Clouds Changes Astronomers Outlook On Starbirth

Molecular hydrogen in the Whirlpool Galaxy M51. The blueish features show the distribution of hydrogen molecules in M51, the raw material for forming new stars. The PAWS team has used this data to create a catalogue of more then 1,500 molecular clouds. The background is a color image of M51 by the Hubble Space Telescope. Superimposed in blue is the CO(1-0) radiation emitted by carbon monoxide (CO) molecules, as measured for the PAWS study using the millimeter telescopes of the Institut de Radioastronomie Millimétrique. The CO molecules are used as tracers for molecular hydrogen. Credit: PAWS team/IRAM/NASA HST/T. A. Rector (University of Alaska Anchorage)

It didn’t happen overnight. By studying the properties of giant molecular clouds in the Whirlpool Galaxy for several years with the millimeter telescopes of IRAM, the Institut de Radioastronomie Millimétrique, astronomers have been given a whole, new look at star formation. Encompassing 1,500 maps of molecular clouds, this new research has found these building blocks of future suns to be encased in a sort of molecular hydrogen mist. This ethereal mixture appears to be far denser than speculated and is found throughout the galactic disc. What’s more, it would appear the pressure created by the molecular fog is a critical factor in determining whether or not stars are able to form within the clouds.

Stars form in the molecular clouds housed within all galaxies. These formations are vast areas of hydrogen molecules with masses which total from a thousand to several million times that of the Sun. When an area of the cloud folds under the weight of its own gravity, it collapses. Pressure and temperature rise and nuclear fusion begins. A star is born.

This exciting new research is changing the way astronomers think about starbirth regions. Study leader Eva Schinnerer (Max Planck Institute for Astronomy) explains: “Over the past four years, we have created the most complete map yet of giant molecular clouds in another spiral galaxy similar to our own Milky Way, reconstructing the amounts of hydrogen molecules and correlating them with the presence of new or older stars. The picture that is emerging is quite different from what astronomers thought these clouds should be like.” The survey, known as PAWS, targeted the Whirlpool galaxy, also known as M51, at a distance of about 23 million light-years in the constellation Canes Venatici – the Hunting Dogs.

Annie Hughes, a post-doctoral researcher at MPIA involved in the study, says: “We used to think of giant molecular clouds as solitary objects, drifting within the surrounding interstellar medium of rarified gas in isolated splendor; the main repository of a galaxy’s supply of hydrogen molecules. But our study shows that 50% of the hydrogen is outside the clouds, in a diffuse, disk-shaped hydrogen fog permeating the galaxy!”

Not only does the enveloping gas play a critical part in star formation, but galaxy structure does as well. One galactic feature in particular is key – spiral arm structure. They sweep slowly around the core area like hands on a clock and are more populated with stars than the remainder of the galactic disk. Sharon Meidt, another MPIA post-doctoral researcher involved in the study, says: “These clouds are definitely not isolated. On the contrary, interactions between clouds, fog, and overall galactic structure appear to hold the key to whether or not a cloud will form new stars. When the molecular fog moves relative to the galaxy’s spiral arms, the pressure it exerts on any clouds within is reduced, in line with a physical law known as Bernoulli’s principle. Clouds feeling this reduced pressure are unlikely to form new stars. According to the press release, Bernoulli’s law is also thought to be responsible for part of the well-known shower-curtain effect: shower curtains blowing inward when one takes a hot shower, another display of reduced pressure.

Jerome Pety of the Institut de Radioastronomie Millimétrique (IRAM), which operates the telescopes used for the new observations, says: “It’s good to see our telescopes live up to their full potential. A study that needed such extensive observation time, and required both an interferometer to discern vital details and our 30 m antenna to put those details into a larger context, would not have been possible at any other observatory.”

Schinnerer concludes: “So far, the Whirlpool galaxy is one example which we have studied in depth. Next, we need to check that what we have found also applies to other galaxies. For our next steps, we hope to profit from both the extension NOEMA of the compound telescope on the Plateau de Bure and from the newly opened compound telescope ALMA in Chile, which will allow in-depth studies of more distant spiral galaxies.”

Original Story Source: Max Planck Institute for Astronomy News Release.