Astronomers See a Baby Triple-star System Forming

triple star birth
Combined ALMA and VLA image of L1448 IRS3B system. This is the first time astronomers have seen the process that forms binary and triple star systems, called "disk fragmentation". Bill Saxton, ALMA (ESO/NAOJ/NRAO), NRAO/AUI/NSF.

Stars are born in giant clouds of gas and dust. Usually, they're born in batches of two or three or even dozens of babies all in the same créche. Since star birth is often a hidden activity, taking place behind the veil of the birth cloud, it's tough to watch it happen. It also lasts a long time, compared to our short lives. So, astronomers found ways to peer into the places where stars form. One of those methods is to use radio waves emitted from the region which pass right through the birth clouds.

The radio data are then formulated into an "image" that shows us what it looks like if you had radio detectors instead of eyes.

The Triple-star Birth

Astronomers used the Atacama Large Millimeter Array (ALMA) in Chile to peek into a star birth creche. What they found was amazing: a rare triple-star system in the process of forming. It's surrounded by a spiral-shaped cloud of gas and dust and is giving them a good look at the process that creates multiple star systems.

When a Disk Fragments

Stars form as a cloud of gas and material starts gathering material at its heart. This process can take millions of years from the first "push" of the cloud until the young star starts to shine. Here's how it works: first, the cloud is "spurred" into action. This might happen when a nearby supernova explodes and sends shock waves through the cloud. That's usually enough to get things moving.

Once the cloud is in motion, more and more material is pulled into the heart of the cloud where the newborn star will form.

Things get hotter and hotter as more material collects. The cloud starts moving around the star and flattens into a disk. In the case of single-star systems, the disk creates one star. If the disk is massive, the resulting star could also be massive. The cloud can break apart or "fragment" as the spinning continues.

The fragments can form additional stars, all rotating around each other and/or a common center of gravity. Eventually, their birth cloud is used up, dissipates, or it might have enough material left to form planets. The birth of planets is iffy in multiple-star systems, since the gravity of the stars might be enough to disrupt planetary formation. In any case, astronomers aren't quite sure exactly what causes the fragmentation, but it does seem to be part of the formation of binary stars and triple-star systems.

It's tough for optical telescopes to see any of this process while the stars are still encased in their birth clouds. Hubble Space Telescope has given the best views, but even it can't see through the clouds as well as a radio or infrared observatory can. So, radio telescopes such as ALMA, as well as infrared-sensitive observatories such as the Spitzer Space Telescope are used to look at the heated clouds and proto-stars in the créches. Each different wavelength of light used to examine the scene reveals details about the activity that would go undetected by optical telescopes.

In the case of the newborn triple-star system seen by ALMA, the radio emissions show that there's a "dominant" star that has formed along with two companions.

It's relatively rare to see systems like this forming, so the ALMA data is a big step forward in revealing the secrets of the birth of multiple-star systems. It is also the first time astronomers have seen disk fragmentation at work. 

Continuing the Search

The ALMA results aren't the first instance of people noticing disks of material around baby multiple star systems. This has been observed before, but the resolution of the telescopes wasn't enough to tease out details. Resolution is a measure of how clearly an instrument, camera, or telescope can make out an object. High-resolution instruments can see very fine details in celestial objects, while lower-resolution instruments only give us rough images of the targets. Think of it this way: if you wear glasses, you can see things sharply and clearly.

If you look at something through a telescope, it not only magnifies what you see, but gives you more details. The high resolution of the ALMA radio telescope array gives astronomers a chance to look through clouds of gas and dust and see the outlines of newborn stars and their birth environments. If you could be there with a camera, it would give you sharp "optical" views of the same scene, too.

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Petersen, Carolyn Collins. "Astronomers See a Baby Triple-star System Forming." ThoughtCo, Mar. 2, 2017, thoughtco.com/baby-triple-star-system-forming-4109364. Petersen, Carolyn Collins. (2017, March 2). Astronomers See a Baby Triple-star System Forming. Retrieved from https://www.thoughtco.com/baby-triple-star-system-forming-4109364 Petersen, Carolyn Collins. "Astronomers See a Baby Triple-star System Forming." ThoughtCo. https://www.thoughtco.com/baby-triple-star-system-forming-4109364 (accessed December 14, 2017).