A tidal dwarf galaxy has been the target of an international research team. Find out how their discoveries challenge what we thought we knew about how stars form.
Even though it’s bitterly cold here this time of year, January offers some advantages for stargazers like me. One is that it gets dark much earlier, which means I can revel in the beauty of the night sky without having to stay up half the night.
The other advantage is that the big, bright, beautiful constellation of Orion dominates the winter sky. It’s impossible to miss on a frigid January evening, and it offers something for amateur astronomers at every level.
One of the most exciting features of this quintessential winter constellation is the Orion Nebula. It’s not hard to spot because it’s visible to the naked eye, just below Orion’s sword, unlike many nebulas.
Frosty Nights Looking Through My Telescope
I’ve spent quite a few frosty nights looking through my telescope admiring this nebula. It fascinates me and many others because it’s the closest place to Earth where we can see stars forming.
There are several hundred billion stars in our galaxy, and there are several hundred billion galaxies in the Universe. You’d think that with all those observable stars to study, we’d have a pretty good idea of the origin of stars.
The truth is that there’s still a lot about star formation that astronomers can’t explain. They know most of the basics, like the fact that stars form out of dust and molecules suspended in gas clouds.
Stars Form out of Dust and Molecules in Gas Clouds
Even so, scientists still wrestle with what causes clumps in these molecular clouds to collapse, triggering nuclear fusion and starlight. Since star formation is such a vital part of our own origin story, astrophysicists are eager to gain a fuller understanding of the star formation process.
A team of researchers from the University of Bath and the National Astronomical Observatory (OAN) in Madrid have just published a study in the journal Astronomy and Astrophysics. It unravels much of the mystery behind star formation by focusing on a tiny galaxy-class called tidal dwarf galaxies.
When the Universe was young, galaxies were smaller and more plentiful. This extra traffic led to frequent and spectacular galactic collisions.
Tidal Dwarf Galaxies Give Chance to See Process
Tidal dwarf galaxies offer the opportunity to witness the process by which small gaseous galaxies organize themselves into cohorts of brilliant, young stars. The investigators looked at one particular tidal dwarf galaxy called TDG J1023+1952.
They observed it using the world’s most extensive radiotelescope configuration. It’s called the Atacama Large Millimeter Array (ALMA), and the astronomy committee built it in Chile.
The team focused on a tidal dwarf galaxy because they form from the debris generated when two galaxies forcefully collide. This formation history replicates what conditions were like in the early Universe.
Replicates Conditions in the Early Universe
After the collision, the galaxies release some of their gases into nearby space. The gas often collapses under its own gravity. The collapsed gas forms a new galaxy with much less mass than its parent galaxy.
The other difference between a tidal dwarf galaxy and more typical galaxies is that they don’t contain any dark matter. The lack of dark matter affords the scientists the chance to test their theories in an extremely dynamic setting.
Because of this, scientists consider tidal dwarf galaxies to be a pristine environment. Our Milky Way Galaxy formed about 13.6 billion years ago under somewhat similar conditions.
“Violent Gas-Rich Galactic Collision”
Professor Carole Mundell is the University of Bath’s head of Astrophysics. She explained, “The little galaxy we’ve been studying was born in a violent, gas-rich galactic collision and offers us a unique laboratory to study the physics of star formation in extreme environments.”
Some of the study results confirmed existing beliefs, while others came as a surprise to the investigators. For instance, they found molecular clouds in the dwarf tidal galaxy that were very consistent with our galaxy’s molecular clouds.
The molecular clouds aren’t only the same size, but they also have roughly the same contents. These similarities strongly imply that the same star formation process we observe in places like the Orion Nebula is going on everywhere in the Universe.
Gas is Diffuse and Spread Throughout the Galaxy
On the other hand, the scientists also found that the tidal dwarf galaxy gases weren’t all condensed into clouds like they’re used to seeing in our galaxy. Instead, much of the gas is diffuse and spread throughout the galaxy under study.
Professor Mundell explained, “The fact that molecular gas appears in both cloud form and as diffuse gas was a surprise.” The study’s lead author is Dr. Miguel Querejeta from the OAN. He added that “This most likely means most of the molecular gas in this tidal dwarf galaxy is not involved in forming stars, which questions popular assumptions about star formation.”
For example, in addition to the diffuse gas the team observed in the tidal dwarf galaxy, they also saw molecular clouds where no stars seemed to be forming. The lack of protostars isn’t consistent with our current understanding of how stars form.
Universe Has a Remarkable Self-organizing Quality
Our Universe has a remarkable self-organizing quality about it. The more we learn about stars and galaxies, the more we discover that there are patterns at work that reveal themselves everywhere we look.
All of the chemical elements in the Periodic Table we learned about in high school come from the stars. That includes all of the atoms and molecules that make up our own bodies.
Singer-songwriter Joni Mitchell was an art major, but she was right when she wrote, “we are stardust, we are golden.” Gold forms in space when two neutron stars collide.
“We are Stardust. We are Golden”
Every culture has a cosmology and a creation story. With the dawn of the enlightenment, our modern civilization lost its traditional origin stories. Our storytellers have yet to replace them.
Work like the research this team has generated moves us closer to understanding galaxies and stars’ origins. In time, we will have a new science-based story that can give our lives meaning again.
Professor Mundell wrapped things up by saying, “It’s remarkable that we can now study stars and the gas clouds from which they are formed in a violent extragalactic collision with the same detail that we can study those forming in the calm environment of our own Milky Way.”
We always have more to learn if we dare to know.
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