APOD: M33: Triangulum Galaxy (2017 Nov 30)

[APOD Robot]

M33: Triangulum Galaxy

Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp composite image nicely shows off M33's blue star clusters and pinkish star forming regions along the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 7 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

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[Ann]

I like how the picture brings out the relative faintness of the old and intermediate populations of M33. This is a very different galaxy than the Milky Way or Andromeda.

Ann

[BDanielMayfield]

This is a very different galaxy than the Milky Way or Andromeda.

Yes. Most notably, M33 shows almost no central bulge. Why might this be?

[Boomer12k]

Really nice...

:---[===] *

[Ann]

This is a very different galaxy than the Milky Way or Andromeda.

Yes. Most notably, M33 shows almost no central bulge. Why might this be?

I have seen other pictures of M33 where the yellow center has been more notable. Nevertheless, the bulge, if there is one, is small and faint.

Possible reasons for this:

1) The galaxy is small. Most predominantly blue galaxies are small. Small, light-weight elliptical galaxies, which are "all bulge" since they contain no young stars, may also be small and faint (i.e., they therefore have small and faint bulges). Please note that a small, light-weight elliptical galaxy may still moderately massive. That is because small red and yellow stars are "massive for their light output", whereas young blue stars are "brilliant for their mass". Also, of course, dwarf galaxies often contain a lot of dark matter.

2) M33 may have had a history of intermittent star formation. The galaxy may have been "quiet" for long periods, when it would not have experienced any buildup of its bulge.

3) If M33 has had a history of intermittent star formation, it might have been more than usually active lately, which would make it seem to be currently dominated by a relatively bright, young and blue population. But the bulge may still be faint. Since the stars making up the yellow bulge are on average a lot fainter than the young blue population, it takes either many bursts of intense star formation or long, extended periods of low-level star formation to build up a bright old yellow bulge. M33 may have had neither.

Ann

[sillyworm2]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

[sallyseaver]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

[geckzilla]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

Correlation, or causation?

[Ann]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

I wouldn't make such an assumption. Most galaxies contain at least some very old stars, which suggests that at least some parts of the galaxy have been around for a long time. To the best of my knowledge, astronomers have not yet found a truly young galaxy.

Whether or not a galaxy has a large bulge depends, in my amateur opinion, on whether or not it has experienced either of these star formation histories:

a) One mega-massive super-duper burst of star formation, the kind of which is only seen in the very early universe and its ultra luminous infrared galaxies (galaxies which are choking in dust because of their almost impossibly massive bursts of star formation).

b) Many relatively massive bursts of star formation.

c) A slow, steady rate of star formation that goes on for billions of years, creating new stars whose low-mass members will build up the galactic bulge (and whose very massive stars may contribute to the mass of the galaxy's central black hole).

If a galaxy has never experienced a truly super-massive burst of star formation, or if its relatively massive bursts of star formation have been too few, or if the galaxy has not experienced a steady, uninterrupted rate of star formation for billions of years, then the galaxy may not develop a bright bulge at all.

Please note that M33 does have a bulge, or at the very least, it does have a yellow center. The center of M33 is much yellower than the bar of the Large Magellanic Cloud, for example. So M33 has been more efficient than LMC when it comes to building up a yellow center.

Ann

[sallyseaver]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

Correlation, or causation?

Currently, the literature claims that the consistency of this relation implies a "feedback mechanism" which has yet to be identified. At some point, with my research (and Mass Vortex Theory) that there is a causal relationship.

[sallyseaver]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

I wouldn't make such an assumption. Most galaxies contain at least some very old stars, which suggests that at least some parts of the galaxy have been around for a long time. To the best of my knowledge, astronomers have not yet found a truly young galaxy.

Whether or not a galaxy has a large bulge depends, in my amateur opinion, on whether or not it has experienced either of these star formation histories:

a) One mega-massive super-duper burst of star formation, the kind of which is only seen in the very early universe and its ultra luminous infrared galaxies (galaxies which are choking in dust because of their almost impossibly massive bursts of star formation).

b) Many relatively massive bursts of star formation.

c) A slow, steady rate of star formation that goes on for billions of years, creating new stars whose low-mass members will build up the galactic bulge (and whose very massive stars may contribute to the mass of the galaxy's central black hole).

If a galaxy has never experienced a truly super-massive burst of star formation, or if its relatively massive bursts of star formation have been too few, or if the galaxy has not experienced a steady, uninterrupted rate of star formation for billions of years, then the galaxy may not develop a bright bulge at all.

Please note that M33 does have a bulge, or at the very least, it does have a yellow center. The center of M33 is much yellower than the bar of the Large Magellanic Cloud, for example. So M33 has been more efficient than LMC when it comes to building up a yellow center.

Ann

Ann, From my perspective, the statement which you highlighted in red is a claim, not an assumption. In order to justify my claim, however, requires theoretical development beyond the scope of what I can do in a forum post. An assumption is more like an axiom or an assumed truth. Usually axioms should be simple and noncontroversial. -- Sally

[BDanielMayfield]

Does the size of the existing Black Hole at the center of M33 determine the size of the central bulge?

Yes. The bulge takes time to develop in the lifecycle of a galaxy. Once the bulge forms, the mass of the black hole is .1% of the mass of the bulge. This is the updated Magorrian relation, which you can find in Wikipedia under M-sigma relation.

I believe that M33 is too young to have a fully developed bulge.

Correlation, or causation?

Excellent question geck. I look forward to being enlightened by this discussion.