Podcaster: Richard Drumm
Title: UNAWE Space Scoop – A Fossil Galaxy in the Outskirts of Andromeda
Organization: 365 Days Of Astronomy
Description: Space scoop, news for children.
An international team of astronomers found a dwarf galaxy in the outskirts of the Andromeda Galaxy, M31, located over 2.5 million light-years from us. However, the ultra-faint dwarf galaxy, now called Pegasus V, was first spotted by a very attentive amateur astronomer Giuseppe Donatiello, of UAI, the Unione Astrofili Italiani.
The UAI translates as the Union of Italian Amateur Astronomers, and its members are both amateur and professional astronomers. He was looking at an image from the DESI Legacy Imaging Survey, which is done to find targets of interest for DESI, the Dark Energy Spectroscopic Instrument.
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This is the 365 Days of Astronomy Podcast. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
A fossil galaxy in the outskirts of Andromeda
An international team of astronomers found a dwarf galaxy in the outskirts of the Andromeda Galaxy, M31, located over 2.5 million light-years from us.
However, the ultra-faint dwarf galaxy, now called Pegasus V, was first spotted by a very attentive amateur astronomer Giuseppe Donatiello, of UAI, the Unione Astrofili Italiani.
The UAI translates as the Union of Italian Amateur Astronomers, and its members are both amateur and professional astronomers.
He was looking at an image from the DESI Legacy Imaging Survey, which is done to find targets of interest for DESI, the Dark Energy Spectroscopic Instrument.
That instrument is mounted on the 4 meter diameter Mayall Telescope at the Kitt Peak National Observatory near Tucson, Arizona..
Donatiello found a ‘smudge’ described as “a partially resolved over-density” of stars.
This was later confirmed to be a super-faint dwarf galaxy, using observations from the Gemini North telescope in Hawaii.
It was considered to be possible that the dwarf galaxy could be orbiting either M31 at 240 kiloparsecs distance from it, or the Triangulum Galaxy, M33 at 400 kiloparsecs.
The November 1st & 25th, 2011 observations with Gemini showed that Pegasus V seems to have very little of the heavy chemical elements that normally appear in dwarf galaxies.
Because of that, astronomers believe the galaxy is very old and is likely to be a fossil of the first galaxies in the Universe, dating from a time before supernovae had enriched the Universe with heavy metals.
Very faint galaxies are ‘cosmic fossils’ of very old galaxies, as they contain clues to the formation of the Universe’s first stars.
Finding these very old and faint galaxies is a very hard task. Astronomers have not found as many of these ‘fossils’ as their theories predicted.
If there aren’t as many of them, maybe they’ll have to rethink their theories about cosmology and dark matter.
It could be, though, that with these galaxies being small and faint that only the ones that are relatively close to us are going to be found.
And Pegasus V is close, it’s part of our Local Group of galaxies.
In the show notes for today’s podcast I’ve included a link to the scientific paper on the discovery of Pegasus V.
In there you can see the image that Donatiello was presented with when he made his discovery as well as the followup image that the professionals got with the Gemini North Observatory.
It’s a wonder he saw anything at all!
These galaxies have very few of the bright stars that attract our attention and that astronomers use to spectroscopically measure their distances.
This type of galaxy can help us to understand how galaxies form, and also to understand if what we think we know about dark matter is right.
Hey, here’s a cool fact:
Pegasus V is so named because it’s the fifth dwarf galaxy discovered in the constellation Pegasus. It’s the Roman numeral V for the number 5.
But Pegasus is a different constellation from Andromeda, you might well say. And you’d be quite right!
Pegasus V is over 18° away from M31 in the sky, so it’s rather distant from the Andromeda Galaxy.
M31 has at least 13 dwarf galaxies orbiting it and due to the fact that this fine grand design spiral galaxy is close to us, its associated dwarf galaxies are spread over a large swath of the night sky.
Andromeda’s orbiting satellite galaxies are found in the constellations Andromeda, of course, and Cassiopeia, Pisces, Lacerta, Perseus and Pegasus!
But Pegasus V is not the first dwarf galaxy spotted by Donatiello.
In 2016, using his own telescope’s data from 2010 & 2013, in the constellation Andromeda he spotted a dwarf spheroidal galaxy.
It’s near the galaxy NGC 404, which is called “Mirach’s Ghost” after the bright, nearby star Mirach.
The dwarf galaxy, separated from and possibly orbiting the Ghost by a whopping 211,000 light years, is now called Donatiello 1 in his honor.
How cool is that?
Thank you for listening to the 365 Days of Astronomy Podcast!
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365 Days of Astronomy
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