APOD: NGC 7814: Little Sombrero with Supernova (2021 Jul 22)

[APOD Robot]

NGC 7814: Little Sombrero with Supernova

Explanation: Point your telescope toward the high flying constellation Pegasus and you can find this expanse of Milky Way stars and distant galaxies. NGC 7814 is centered in the pretty field of view that would almost be covered by a full moon. NGC 7814 is sometimes called the Little Sombrero for its resemblance to the brighter more famous M104, the Sombrero Galaxy. Both Sombrero and Little Sombrero are spiral galaxies seen edge-on, and both have extensive halos and central bulges cut by a thin disk with thinner dust lanes in silhouette. In fact, NGC 7814 is some 40 million light-years away and an estimated 60,000 light-years across. That actually makes the Little Sombrero about the same physical size as its better known namesake, appearing smaller and fainter only because it is farther away. In this telescopic view from July 17, NGC 7814 is hosting a newly discovered supernova, dominant immediately to the left of the galaxy's core. Cataloged as SN 2021rhu, the stellar explosion has been identified as a Type Ia supernova, useful toward calibrating the distance scale of the universe.

<< Previous APOD

This Day in APOD

Next APOD >>

[Ann]

NGC 7814: Little Sombrero with Supernova. NGC 7814 is a galaxy with no star formation and no massive stars. Image Credit & Copyright: CHART32 Team.

---

NGC 4631. This is a galaxy chock full of star formation and massive stars. Photo: R Jay GaBany.

---

Note the difference between NGC 7814 and NGC 4631. The former galaxy has an almost razor-thin, almost perfectly straight central dust lane. The galaxy looks perfectly symmetrical and undisturbed, and its colors are yellow. This is a perfect example of a galaxy that contains no star formation and no massive stars.

NGC 4631, by contrast, contains so much star formation and so many "angry" massive stars that the entire galaxy looks contorted.The central dust lane has been separated into a million little pieces. And the color of the galaxy is mostly blue.

If there is a supernova in a galaxy like NGC 7814, our jaws would drop to the floor if it was a core-collapse supernova. Because such a supernova requires a massive progenitor star, like, say, Betelgeuse or Rigel, and where do you find such a star in NGC 7814?

So you can tell at a glance, by looking at the galaxy, that this has to be a supernova type Ia, whose progenitor star is a white dwarf. Because of course there are white dwarfs in NGC 7814. There are white dwarfs in all and every galaxy, since they are the remnants of moderate-mass stars, and you can't find a galaxy anywhere that hasn't had a relatively abundant population of stars like Sirius and even the Sun.

A type Ia supernova occurs when a massive white dwarf, which is balancing precariously close to its Chandrasekhar limit, beyond which its electron pressure can no longer support it, receives an unwelcome helping of additional mass from a companion star that completely unsettles it and makes it go bang.

A core-collapse supernova, by contrast, happens when a massive star has exhausted all its ways of producing energy in its core to hold itself up and prevent itself from collapsing. When such a star has run through all its various ways of fusion and core shrinking and can go no further because it has an iron core, it collapses and goes out with a bang.

Galaxy M65. Photo: NOIRLab.

---

Closeup of parts of M65, with small numbers of scattered massive blue stars. ESA/Hubble & NASA - http://www.spacetelescope.org/images/potw1352a/

---

M65 with supernova.png

Supernova SN 2013am in M65.

Fascinatingly, there is a Messier galaxy that contains very few massive stars, but it has nevertheless produced a core-collapse supernova. That galaxy is M65. In the picture at left, you can see a tiny bluish spot to the lower right of the galaxy's center. That is (probably) a cluster of massive blue stars (or possibly a foreground binary blue star). To the lower left of that blue spot there are even fainter hints of blue. This bluish color comes from scattered massive stars.

On March 21, a supernova appeared in M65. The supernova got the designation SN 2013am, and it turned out to be a core-collapse supernova.

But normally a galaxy like M65 would produce a supernova of type Ia, not a core-collapse supernova. Well, unexpected things happen!

Ann

[VictorBorun]

If there is a supernova in a galaxy like NGC 7814, our jaws would drop to the floor if it was a core-collapse supernova. Because such a supernova requires a massive progenitor star, like, say, Betelgeuse or Rigel, and where do you find such a star in NGC 7814?

Ann

But once in a while can a 10 billion years old double stellar system in an old red and yellow galaxy collide with a third star, make a merge into a large star, burn the matter to iron and then make a core-collapse supernova?

[orin stepanek]

NGC7814_SN_Volker_54.jpg

Hot spot in little sombrero!🥵

[VictorBorun]

NGC7814_SN_Volker_54.jpg

Hot spot in little sombrero!🥵

"the jewel in the sombrero" (that jewel is not for ever)

The brichtest jewel in my crown
Wad be, wad be my Queen.

[MarkBour]

Well, that is certainly a nice supernova shot!
In one of the links regarding the supernova, there is an interesting plot of its spectrum

>>>>https://www.wis-tns.org/object/2021rhu<<<<

Capture1.PNG

I don't know anything about reading this spectrum to determine what is present.
The table below the image lists: H, He, C, N, O, Na, Mg, Si, S, Ca, Fe
but I don't think the table was implying that all of these are indeed observed in that spectrum.

I'd certainly be grateful if someone were to explain what that spectrum actually shows.

[johnnydeep]

Ann, you said several times in your post in no uncertain terms that NGC 7814 contained no star formation and no massive stars, but in a huge galaxy like this, can we really be so certain? Sure, maybe it has a lot less star formation than other galaxies, but absolutely none at all? Seems highly improbable to me.

[Ann]

Ann, you said several times in your post in no uncertain terms that NGC 7814 contained no star formation and no massive stars, but in a huge galaxy like this, can we really be so certain? Sure, maybe it has a lot less star formation than other galaxies, but absolutely none at all? Seems highly improbable to me.

No, Johnny, we can't be so certain. Low-mass star formation, that doesn't require a lot of raw material to happen and doesn't produce any high-mass stars, could well occur without us noticing it from a distance of tens of millions of light-years.

The fact that NGC 7814 does have a central dust lane tells us that there are indeed concentrations of gas and dust in NGC 7814, and there may indeed be dense enough pockets of it to allow low-mass star formation to take place.

Ann

[johnnydeep]

Ann, you said several times in your post in no uncertain terms that NGC 7814 contained no star formation and no massive stars, but in a huge galaxy like this, can we really be so certain? Sure, maybe it has a lot less star formation than other galaxies, but absolutely none at all? Seems highly improbable to me.

No, Johnny, we can't be so certain. Low-mass star formation, that doesn't require a lot of raw material to happen and doesn't produce any high-mass stars, could well occur without us noticing it from a distance of tens of millions of light-years.

The fact that NGC 7814 does have a central dust lane tells us that there are indeed concentrations of gas and dust in NGC 7814, and there may indeed be dense enough pockets of it to allow low-mass star formation to take place.

Ann

But absolutely no massive star formation? Wouldn't that just require, what, 20 - 50 times more gas? Or are there other factors that are needed in order for massive stars to form that can't possibly be happening in NGC 7814? Couldn't there be some massive stars forming or even already existing concealed from our detection by dust?

[Chris Peterson]

Ann, you said several times in your post in no uncertain terms that NGC 7814 contained no star formation and no massive stars, but in a huge galaxy like this, can we really be so certain? Sure, maybe it has a lot less star formation than other galaxies, but absolutely none at all? Seems highly improbable to me.

No, Johnny, we can't be so certain. Low-mass star formation, that doesn't require a lot of raw material to happen and doesn't produce any high-mass stars, could well occur without us noticing it from a distance of tens of millions of light-years.

The fact that NGC 7814 does have a central dust lane tells us that there are indeed concentrations of gas and dust in NGC 7814, and there may indeed be dense enough pockets of it to allow low-mass star formation to take place.

Ann

But absolutely no massive star formation? Wouldn't that just require, what, 20 - 50 times more gas? Or are there other factors that are needed in order for massive stars to form that can't possibly be happening in NGC 7814? Couldn't there be some massive stars forming or even already existing concealed from our detection by dust?

I think you are correct. There is no galaxy, no matter how anemic, where large mass stars are not forming. They just aren't doing so in large numbers or in large, dense regions.

[Ann]

No, Johnny, we can't be so certain. Low-mass star formation, that doesn't require a lot of raw material to happen and doesn't produce any high-mass stars, could well occur without us noticing it from a distance of tens of millions of light-years.

The fact that NGC 7814 does have a central dust lane tells us that there are indeed concentrations of gas and dust in NGC 7814, and there may indeed be dense enough pockets of it to allow low-mass star formation to take place.

Ann

But absolutely no massive star formation? Wouldn't that just require, what, 20 - 50 times more gas? Or are there other factors that are needed in order for massive stars to form that can't possibly be happening in NGC 7814? Couldn't there be some massive stars forming or even already existing concealed from our detection by dust?

I think you are correct. There is no galaxy, no matter how anemic, where large mass stars are not forming. They just aren't doing so in large numbers or in large, dense regions.

Well, yes. Every spiral galaxy that contains dust - and possibly also some elliptical galaxies - probably form at least some massive stars.

NGC 7814. Photo: CHART32 Team.

---

NGC 3190. Image: Hubble Legacy Archive, ESA, NASA, Robert Gendler.

---

These two galaxies, NGC 7814 and NGC 3190, appear to be completely yellow and completely devoid of star formation in moderately low-resolution images. But as you can see, the central dust lane of NGC 3190 is a lot more disturbed than the dust lane of NGC 7814. To me, that suggests that it is more likely that NGC 3190 contains some star formation and massive stars than that the same thing is true for NGC 7814.

If you go to this page, you can see larger versions of the image of NGC 3190, which do seem to show scattered blue stars in the galaxy's disk, and even at least one association of blue stars.

NGC 1316. Image: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

---

So a somewhat disturbed central dust lane is often a sign of star formation, but the dust lane probably shouldn't be too scattered and thin. So is there any star formation in the dust lanes of elliptical galaxy NGC 1316?

Go to this page to see a 13 MB version of the picture of NGC 1316. It is indeed possible to see some small blue dots in the "body" of NGC 1316, and a few of these blue dots do look like stars. And maybe possibly maybe there are hints of blue next to the darkest dust bunny at the center of NGC 1316, as if massive stars have indeed just formed there.

Ann

[johnnydeep]

For Ann:

Maybe a blue spot in a Hubble image of NGC 7814:

AEEF96C2-879D-4898-9FB4-F9CA6FCC4582.jpeg

This is a closeup of the upper right area of this big Hubble pic:

https://www.nasa.gov/sites/default/file ... w1505a.jpg

(From https://www.nasa.gov/content/goddard/hu ... e-sombrero)

0A7BD4A3-BB9B-44A5-85F4-EC164039C1D9.jpeg