Newborn stars are shrouded in dust clouds, making them a mystery to science. Find out how a radio telescope survey has shed light on how solar systems form.
The first constellation I learned to recognize as a child was Orion. It dominates the night sky during our long winter nights here in Canada.
In traditional star lore, Orion is the figure of a hunter, with broad shoulders, a belt, a sword and long legs. Orion’s sword is a little line of three stars and a bright nebula.
It’s called the Orion Nebula. You can see it with the naked eye if you get away from bright city lights.
MOST PROMINENT EXAMPLE OF A STELLAR NURSERY
When my stargazing got a bit more ambitious, I started aiming my telescope at the nebula itself. It’s about 20 light-years across, making it the most prominent example in our night sky of a stellar nursery, i.e., a star-forming region full of infant stars.
The Orion Nebula is the most visible part of a much bigger nebula called the Orion Molecular Cloud Complex. The complex is huge, covering the whole constellation of Orion.
The complex includes quite a few other famous nebulae like Barnard’s Loop, the Horsehead Nebula and the Flame Nebula. The whole complex is teeming with star formation, most of which happens in the dense clouds like the Orion Nebula.
WHOLE COMPLEX TEEMING WITH STAR FORMATION
Stellar nurseries are cold clouds of gas and dust called molecular clouds. The gas and dust aren’t evenly distributed within the clouds and clumps form.
These clumps get denser and denser until eventually, those areas in the cloud collapse under their own gravity and stars are born. Astronomers call new newborn stars at this stage protostars.
Protostars start to spin during this process and that causes a disk to form around them. Planets, including our Earth, form out of those disks around most newborn stars.
PLANETS FROM OUT OF THE DISKS AROUND PROTOSTARS
There’s a range of different forms the young star can take. If the clump is very small, it won’t ignite and it remains a brown dwarf.
Brown dwarfs aren’t quite stars and they’re not really planets either. They emit some infrared radiation, but nothing like the energy that we get from our sun. They have atmospheres something like the gas giants in our solar system.
Otherwise, the collapsing dust and gas start a process of nuclear fusion, converting hydrogen into helium. The fusion sends pressure out from the centre of the newborn star, which counterbalances the star’s gravity and stabilizes it.
COLLAPSING DUST AND GAS START NUCLEAR FUSION PROCESS
At that point, it becomes a main-sequence star, which includes about 90% of the stars in the night sky. A star’s lifespan depends on its mass.
Massive stars burn out faster than stars with less mass. Their extra gravity makes their cores hotter and they burn through their fuel in less time than an average-sized star.
Our sun will be a main-sequence star for about 10 billion years. Stars that have ten solar masses or more last less than 20 million years.
OUR SUN WILL BE A MAIN SEQUENCE STAR FOR 10 BILLION YEARS
Meanwhile, stars that are half the size of the sun can last up to 100 billion years. That’s about seven times longer than the age of the universe.
The lives of main-sequence stars end when they use up their fuel. Smaller red dwarf stars just quietly shut down and turn into white dwarfs.
Medium-sized stars like the sun turn into red giants when they start running out of fuel. They expand in volume for a time and then collapse back into white dwarfs as well.
MOST MASSIVE STARS GO OUT WITH A SUPERNOVA EXPLOSION
The sun will swallow up the inner planets when its time to become a red dwarf arrives. The most massive stars go out with a bang, creating a supernova explosion.
Astronomers at the National Radio Astronomy Observatory have been concentrating on the Orion Clouds, capturing images of more than 300 newborn stars and their planet-forming disks.
For a long time, scientists have wanted a better understanding of how young stars form planetary disks. It’s hard to see these disks because young stars are very faint and they’re still surrounded by the leftover dust and gas from their stellar nurseries.
YOUNG STARS AND FAINT AND SURROUNDED BY DUST AND GAS
Instead of optical telescopes or even space telescopes, astronomers have to use techniques that don’t require visible light to study protostars. That’s where radio astronomy comes in.
The team used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) to observe protostars in the Orion Molecular Clouds.
This survey is called VLA/ALMA Nascent Disk and Multiplicity (VANDAM for short). It’s the largest survey of newborn stars and their disks ever done.
MASSIVE PLANETS CAN FORM EARLIER THAN THOUGHT
They found that the disks formed around newborn stars are about the same size, and much more massive than older disks. That suggests that massive planets can form earlier than previously thought
The VANDAM survey also identified four highly irregular shaped protostars. They think their odd shapes mean that they are in the very earliest stages of star formation.
Team member Professor Nicole Karnath of the University of Ohio explained, “We think that they are in one of the earliest stages of star formation and some may not even have formed into protostars yet.”
“SOME MAY NOT EVEN HAVE FORMED INTO PROTOSTARS YET”
As for their age, Professor Karnath went on to say, “We are not entirely sure how old they are, but they are probably younger than ten thousand years.”
Survey leader John Tobin explained that the success of the project was due to the high sensitivity and resolution the VLA and ALMA telescopes deliver. “The combined use of ALMA and the VLA has given us the best of both worlds. Thanks to these telescopes, we start to understand how planet formation begins.”
The way newborn stars form and then give birth to planets is a gap in our understanding of the story of the universe. We know that the stellar nurseries arose out of the Big Bang process, and we have a fairly clear idea of how planets form out of the protoplanetary disks.
MORE THAN 300 EXAMPLES OF PROTOSTARS TO CHOOSE FROM
Until now, it’s been hard to get a glimpse of how stars arise out of the molecular clouds that spawn them. This new survey provides more than 300 examples of protostars to choose from.
This will improve our understanding of where our sun came from and how the various types of stars we can see arose within our galaxy.
We always have more to learn if we dare to know.
National Radio Astronomy Observatory
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey ofOrion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks
Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?
Planets Form From Stardust – Rapidly and Frequently
Unfolding the Milky Way
Are Supermassive Black Holes Collapsed Stars?