APOD: A Halo for Andromeda (2020 Sep 03)

[APOD Robot]

A Halo for Andromeda

Explanation: M31, the Andromeda Galaxy, is the closest large spiral galaxy to our Milky Way. Some 2.5 million light-years distant it shines in Earth's night sky as a small, faint, elongated cloud just visible to the unaided eye. Invisible to the eye though, its enormous halo of hot ionized gas is represented in purplish hues for this digital illustration of our neighboring galaxy above rocky terrain. Mapped by Hubble Space Telescope observations of the absorption of ultraviolet light against distant quasars, the extent and make-up of Andromeda's gaseous halo has been recently determined by the AMIGA project. A reservoir of material for future star formation, Andromeda's halo of diffuse plasma was measured to extend around 1.3 million light-years or more from the galaxy. That's about half way to the Milky Way, likely putting it in contact with the diffuse gaseous halo of our own galaxy.

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[MarkBour]

On the forum discussion just a few days back (August 31), @bystander posted

viewtopic.php?t=40907

In that discussion of a stellar mass black hole, I happened to ask if anyone thought that galactic halos were (at least in part), the products of the relativistic jets of the galactic supermassive black hole. @neufer posted a couple of articles in response, and it seemed like he was perhaps supporting the idea, though I didn't see any direct "yea", "nay", or opinion answer from him.

So here, just a few days later is a fascinating APOD about Andromeda's halo. Considering how hard the AMIGA project had to work to observe Andromeda's halo (they had to look at quasars beyond it to study its absorption behavior) I would guess that this is only the second galactic halo we've been able to study in much detail to date.

Again, my curiosity about the jets from Andromeda's core contributing to this halo arises. Given billions of years, some of the material from the jets could easily have traveled 1-2 million light years.

[Ann]

Elbow bump. Photo: Shutterstock.

---

Our galaxies are doing the elbow bump. Not yet grabbing each other's hands and pulling.

Yellow-looking Andromeda and Comet 64P/Swift-Gehrels.
Photo: Joseph Brimacombe

That enormous halo of hot ionized gas around Andromeda reminds me of the vicinity of red and dead galaxies, because those kinds of halos are exactly what you find in big galaxy clusters jam packed with elliptical galaxies, where star formation has been mostly quelled. I guess it's the outbursts of the huge black hole in the biggest and baddest of all the elliptical galaxies in the cluster that kills most of the star formation in itself and in almost all of its hapless cluster captives, but maybe all that hot gas surrounding them does some of the killing too.

Which brings me to Andromeda, which is a really big galaxy. Really big. And mean, I think. And just look at it, it isn't forming many new stars. At all. Those pictures that you have seen showing all those bright blue stars in Andromeda have been fooling you, because they have been processed to look prettier. Andromeda is clearly on its way to becoming a lenticular galaxy, a disk-shaped yellow galaxy with no star formation. Unless, of course, we hit it first, and it (and we) first become a mess like NGC 6240 and then an elliptical galaxy. Oh well.

Ann

[bystander]

viewtopic.php?t=40948

[heehaw]

I notice, not one word about the dark matter (which is MOST of the matter)!

[De58te]

So question. Some galaxies are 50,000 ly across. Some like the Milky Way are 100,000 ly across, and some are 200,000 ly in size. If the radius of Andromeda's halo is 1.3 million light years, then does that make the size of the Andromeda Galaxy 2.6 million light years across? Is then Andromeda the biggest galaxy measured, or is there an even bigger galaxy?

[orin stepanek]

I takt it these are MW's children; but they seem to follow a ring around Andromeda! I never noticed that in the sky before!

[BDanielMayfield]

I notice, not one word about the dark matter (which is MOST of the matter)!

Not that I doubt DMs really, but it’s easy to ignore or forget something that’s invisible and that has so far defied all attempts to physically explain. MOND might be ill, but it ain’t dead yet.

[Ann]

So question. Some galaxies are 50,000 ly across. Some like the Milky Way are 100,000 ly across, and some are 200,000 ly in size. If the radius of Andromeda's halo is 1.3 million light years, then does that make the size of the Andromeda Galaxy 2.6 million light years across? Is then Andromeda the biggest galaxy measured, or is there an even bigger galaxy?

Wikipedia wrote:

IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster and is one of the largest known galaxies. Its halo extends about 600 kiloparsecs (2 million light-years) from its core, and it has a mass of about 100 trillion stars. The galaxy is located 320 megaparsecs (1.04 billion light-years) from Earth.

An assortment of big galaxies. Both the Milky Way and Andromeda are in there. Credit: Rhys Taylor.

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A number of kind of pretty big galaxies, with IC 1101 in the middle. Credit: Rhys Taylor.

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I don't guarantee that Rhys Taylor, who made the galaxy comparison charts above, got all the galaxy sizes correct. But the pictures should give you an idea, at least.

Ann

[Cousin Ricky]

Wikipedia wrote:

IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster and is one of the largest known galaxies. Its halo extends about 600 kiloparsecs (2 million light-years) from its core, and it has a mass of about 100 trillion stars. The galaxy is located 320 megaparsecs (1.04 billion light-years) from Earth.

That’s a rather imprecise way of stating a mass.

[Cousin Ricky]

How many of you can spot the M33 galaxy in this image?

[Ann]

Wikipedia wrote:

IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster and is one of the largest known galaxies. Its halo extends about 600 kiloparsecs (2 million light-years) from its core, and it has a mass of about 100 trillion stars. The galaxy is located 320 megaparsecs (1.04 billion light-years) from Earth.

That’s a rather imprecise way of stating a mass.

Indeed, that's a good point.

As for the mass of stars, they are surprisingly "not-so-different from one another". That is to say, the mass of stars vary a lot less than the luminosity and temperature of stars. Also we can be pretty sure that most stars in pretty much all galaxies, and most certainly in all large galaxies, belong to spectral classes M and K, and their mass is typically, I would say, between 30% and 50% of the mass of the Sun. So 100 trillion stars would translate to, roughly, 30-50 trillion solar masses.

Of course, most of the mass of a galaxy is in the form of dark matter. I believe there is some 5-6 times more dark matter than baryonic matter in the Universe, and if we assume that the same ratio is found in IC 1101, then the mass of IC 1101 would be some 180-350 trillion solar masses all in all.

Just my amateur guess!

Ann

[johnnydeep]

How many of you can spot the M33 galaxy in this image?

Nice test question! I found it with the help of this prior APOD - https://apod.nasa.gov/apod/ap130926.html :

M31 and M33 In The Sky Together

So, here it is in this APOD of M31's halo:

M31 and Its Halo, and M33 In The Sky Together

From the blurb at https://apod.nasa.gov/apod/ap130926.html:

Separated by about 14 degrees (28 Full Moons) in planet Earth's sky, spiral galaxies M31, left, and M33 are both large members of the Local Group, along with our own Milky Way galaxy. This wide-angle, telescopic mosaic captures colorful details of spiral structure in both, while the massive neighboring galaxies seem to be balanced either side of bright Mirach, beta star in the constellation Andromeda. But M31, the Andromeda Galaxy, is really 2.5 million light-years distant and M33, the Triangulum Galaxy, is also about 3 million light years away. Mirach, just 200 light-years from the Sun, lies well within the Milky Way, along with the dim clouds of dust drifting through the frame only a few hundred light-years above the galactic plane. Although they look far apart, M31 and M33 are locked in a mutual gravitational embrace. Radio astronomers have found indications of a bridge of neutral hydrogen gas that could connect the two, evidence of a closer encounter in the past. Based on measurements, gravitational simulations currently predict that the Milky Way, M31, and M33 will all undergo mutual close encounters and potentially mergers, billions of years in the future.

Note that M33 appears to be just on the edge of M31's halo!

[Ann]

How many of you can spot the M33 galaxy in this image?

I can. It's just skimming the horizon, to the lower right of Andromeda.

Ann

[johnnydeep]

So, how does the AMIGA project know that what its measuring is due to the halo around Andromeda as opposed to the likely halo around the Milky Way through which all the light from the tell-tale quasars must travel before we can measure it?

[neufer]

So, how does the AMIGA project know that what its measuring is due to the halo around Andromeda as opposed to the likely halo around the Milky Way through which all the light from the tell-tale quasars must travel before we can measure it?

• The Milky Way's halo is roughly symmetric all around us and thus
  can be treated as a homogeneous foreground to be digitally removed for clarity.

[MarkBour]

So, how does the AMIGA project know that what its measuring is due to the halo around Andromeda as opposed to the likely halo around the Milky Way through which all the light from the tell-tale quasars must travel before we can measure it?

Great point!

• The Milky Way's halo is roughly symmetric all around us and thus
  can be treated as a homogeneous foreground to be digitally removed for clarity.

Just to be contrary, how safe is this assumption? The conclusion from the AMIGA data is that Andromeda's halo is a complex structure with at least two distinct shells. That variability, in particular, should be suspect if we're just assuming that our halo is uniform. But I haven't studied the Fermi results ... perhaps they give strong evidence that our halo is uniform. Even then, I can scarce imagine our halo would have equal quantity in every direction.

[neufer]

viewtopic.php?t=40907

In that discussion of a stellar mass black hole, I happened to ask if anyone thought that galactic halos were (at least in part), the products of the relativistic jets of the galactic supermassive black hole. @neufer posted a couple of articles in response, and it seemed like he was perhaps supporting the idea, though I didn't see any direct "yea", "nay", or opinion answer from him.

So here, just a few days later is a fascinating APOD about Andromeda's halo. Considering how hard the AMIGA project had to work to observe Andromeda's halo (they had to look at quasars beyond it to study its absorption behavior) I would guess that this is only the second galactic halo we've been able to study in much detail to date. Again, my curiosity about the jets from Andromeda's core contributing to this halo arises. Given billions of years, some of the material from the jets could easily have traveled 1-2 million light years.

• Perhaps...the haloes came first

Cold streams in early massive hot haloes as the main mode of galaxy formation

A. Dekel, Y. Birnboim, G. Engel, J. Freundlich, T. Goerdt, M. Mumcuoglu, E. Neistein, C. Pichon, R. Teyssier & E. Zinger

Nature volume 457, pages451–454(2009)

Abstract: Massive galaxies in the young Universe, ten billion years ago, formed stars at surprising intensities. Although this is commonly attributed to violent mergers, the properties of many of these galaxies are incompatible with such events, showing gas-rich, clumpy, extended rotating disks not dominated by spheroids. Cosmological simulations and clustering theory are used to explore how these galaxies acquired their gas. Here we report that they are ‘stream-fed galaxies’, formed from steady, narrow, cold gas streams that penetrate the shock-heated media of massive dark matter haloes. A comparison with the observed abundance of star-forming galaxies implies that most of the input gas must rapidly convert to stars. One-third of the stream mass is in gas clumps leading to mergers of mass ratio greater than 1:10, and the rest is in smoother flows. With a merger duty cycle of 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. The rarer, submillimetre galaxies that form stars even more intensely are largely merger-induced starbursts. Unlike destructive mergers, the streams are likely to keep the rotating disk configuration intact, although turbulent and broken into giant star-forming clumps that merge into a central spheroid. This stream-driven scenario for the formation of discs and spheroids is an alternative to the merger picture.

[MarkBour]

• Perhaps...the haloes came first

I'd have to accept that as a likely alternative. in particular, concerning dark matter, it would make sense if that came early and helped drive the galaxy formation. This APOD focuses mainly on hot gas. In regard to that, I'm wondering if we can give some accounting of the effect of the central jets over the life of a galaxy.

[TheZuke!]

So, how does the AMIGA project know that what its measuring is due to the halo around Andromeda as opposed to the likely halo around the Milky Way through which all the light from the tell-tale quasars must travel before we can measure it?

The Milky Way doesn't have a halo, because you know, humans occupy The Milky Way, and humans are not angelic!


I do find it amazing, that a computer that has not been made since the mid-1990s is still being used in so much research!
(Amiga)

[neufer]

Click to play embedded YouTube video.

<<Flowers for Algernon is the title of a science fiction short story and a novel by American writer Daniel Keyes. The short story, written in 1958 and first published in the April 1959 issue of The Magazine of Fantasy & Science Fiction, won the Hugo Award for Best Short Story in 1960. The novel was published in 1966 and was joint winner of that year's Nebula Award for Best Novel (with Babel-17).

Algernon is a laboratory mouse who has undergone surgery to increase his intelligence. The story is told by a series of progress reports written by Charlie Gordon, the first human subject for the surgery, and it touches on ethical and moral themes such as the treatment of the mentally disabled.

Although the book has often been challenged for removal from libraries in the United States and Canada, sometimes successfully, it is frequently taught in schools around the world and has been adapted many times for television, theatre, radio and as the Academy Award-winning film Charly.

Characters in the book were based on people in Keyes's life. The character of Algernon was inspired by a university dissection class, and the name was inspired by the poet Algernon Charles Swinburne.[ Nemur and Strauss, the scientists who develop the intelligence-enhancing surgery in the story, were based on professors Keyes met while studying psychoanalysis in graduate school.

In 1958, Keyes was approached by Galaxy Science Fiction magazine to write a story, at which point the elements of Flowers for Algernon fell into place. When the story was submitted to Galaxy, however, editor Horace Gold suggested changing the ending so that Charlie retained his intelligence, married Alice Kinnian, and lived happily ever after.] Keyes refused to make the change and sold the story to The Magazine of Fantasy & Science Fiction instead.>>

[TheZuke!]

<<Flowers for Algernon is the title of a science fiction short story and a novel by American writer Daniel Keyes. The short story, written in 1958 and first published in the April 1959 issue of The Magazine of Fantasy & Science Fiction, won the Hugo Award for Best Short Story in 1960. The novel was published in 1966 and was joint winner of that year's Nebula Award for Best Novel (with Babel-17).

Daniel's daughter worked at the same place I did back in the 1990's.
She was a nice woman. I never met him, but she said he often posted on Internet fora to help budding SF writers.