Mock sausage without the tempeh
Data from a billion stars is impossible to study by humans without the assistance of dedicated computer systems.
“We can’t stare at seven million stars and figure out what they’re doing. What we did in this series of projects was use the Gaia mock catalogs,” Necib explains.
The Gaia mock catalogs, developed by Robyn Sanderson of the University of Pennsylvania, examines what astronomers would see if the FIRE simulations were correct, and seen by GAIA.
“We needed to make sure that we’re not learning artificial things about the simulation, but really what’s going on in the data. For that, we had to give it a little bit of help and tell it to reweigh certain known elements to give it a bit of an anchor,” Necib explains.
The team tested the simulation on known features of the Milky Way, including the Gaia Sausage, a distinct collection of stars once part of a dwarf galaxy, which merged with the Milky Way sometime between six and 10 billion years ago. These stars have a distinct orbital shape, which showed up in the simulations, along with halo stars which give our galaxy its shape, providing evidence the models were correct.
By studying baryons (a class of subatomic particle), the Ananke framework, developed at Northwestern University, models the behavior of stars.
“The Ananke framework generates realistic synthetic stellar surveys from cosmological baryonic simulations… The result is a self-consistent, dust-extincted synthetic survey of each simulated galaxy that leaves intact important observational relationships between gas, dust extinction, stellar populations, and dark matter,” researchers at Northwestern report.
The model also revealed a group of 250 stars traveling toward the center of the Milky Way, while also orbiting around the galaxy.
“The Nyx stars were found on two stages. First through a machine learning algorithm led by my collaborator Bryan Ostdiek, where we trained on the Ananke simulations to distinguish accreted stars (stars born in other galaxies and brought in through mergers) and disk stars, stars born in the Milky Way. After this first run, Bryan handed me a catalog of stars with an accretion score. I then used a clustering algorithm in kinematics to find these particular stars. Said another way, these stars have very specific motion, where they are corotating with the disk of the Milky Way, but they are also going to the center of the galaxy. This is interesting as it would be the first evidence of a merger that happened parallel to the disk,” Necib tells The Cosmic Companion.
Here’s a look at the GAIA mission, and how it is revolutionizing our understanding of the Universe.
When Dr. Necib first saw this data, she assumed the findings were in error, and did not inform her colleagues about the finding for three weeks. During that time, she realized that what she was seeing was real, and brought the data to her fellow researchers.
Necib searched previous findings to see if anyone else had previously discovered this group of stars, and found she was the first researcher to recognize the group. This gave the researcher the chance to name this unusual family of stars. She named the group Nyx, in honor of the Greek Goddess of the night.