Astronomers use a distributed supercomputer to reconstruct an ancient dwarf galaxy

Using the 1.5 PetaFLOPS [email protected] distributed supercomputer, astronomers have calculated the original mass and size of a dwarf galaxy that was shredded in a collision with our own galaxy, the Milky Way, several billion years ago.

Artist’s impression of a dwarf galaxy. Image credit: Rensselaer Polytechnic Institute.

A few dozen dwarf galaxies are known to orbit our Milky Way.

Over billions of years, these dwarf galaxies perturb and stretch around the Milky Way in tidal currents.

The positions and velocities of the stars that make up these fluxes therefore carry information about the gravitational field of the Milky Way.

As such, dwarf galaxies act as gravitational probes to determine the distribution of gravitational mass in the Milky Way.

In 2006, two teams of astronomers independently discovered a new stellar stream by examining the Sagittarius stream. Due to the lack of a visible ancestor, the stream has been named the orphan stream.

The southern part of the flow was later named Chenab before it was discovered that both parts of the flow – now known as the Orphan-Chenab flow – resulted from tidal disturbance from the same dwarf galaxy.

“We’ve done simulations that take this big stream of stars, save it for a few billion years, and see what it looked like before it fell into the Milky Way,” said Prof Heidi Newberg, an astronomer at Rensselaer Polytechnic. Institute.

“We now have a measurement from the data, and this is the first big step towards using the information to find dark matter in the Milky Way.”

To probe the internal structure of the progenitor of the dwarf galaxy of the Orphan-Chenab stream, Professor Newberg and his colleagues used the distributed supercomputer [email protected], a collection of around 26,000 volunteer computers connected by the open infrastructure of Berkeley for network computing, running at 1.5 petaFLOPS of combined computing power.

“It’s a huge problem, and we’re solving it by running tens of thousands of different simulations until we get one that actually matches,” Professor Newberg said.

“And that requires a lot of computing power, which we get with the help of volunteers around the world who are part of [email protected]

“We force it hard, but given the complexity of the problem, I think this method has a lot of merit.”

Astronomers estimate the total mass of the progenitor of the dwarf galaxy whose stars today form the Orphan-Chenab flux at 2*107 times the mass of our Sun.

However, it is estimated that just over 1% of this mass is made up of ordinary matter such as stars.

The rest is thought to be dark matter which exerts a gravitational force, but which we cannot see because it neither absorbs nor emits light.

“Tidal current stars are the only stars in our Galaxy for which it is possible to know their positions in the past,” Professor Newberg said.

“By looking at the current velocities of stars along a tidal current and knowing that they were all in roughly the same place and moving at the same speed, we can determine how much gravity is changing along of this current. And that will tell us where the dark matter is in the Milky Way.

The team also found that the ancestor of the Orphan-Chenab stream has less mass than galaxies measured on the outskirts of the Milky Way today.

“The measured progenitor mass is at the lower end of previous measurements and, if confirmed, lowers the mass range of ultraweak dwarf galaxies,” the authors said.

“Our optimization assumes a fixed Milky Way potential, the orbit of the Orphan-Chenab stream, and a radial profile for the progenitor, ignoring the impact of the Large Magellanic Cloud.”

The study was published in the Astrophysical Journal.


Eric J. Mendelsohn et al. 2022. Estimation of the mass and radial profile of the dwarf galaxy progenitor of the Orphan-Chenab flux using [email protected] ApJ 926, 106; doi: 10.3847/1538-4357/ac498a

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