APOD: Leo Trio (2017 Apr 12)

[APOD Robot]

Leo Trio

Explanation: This group is popular in the northern spring. Famous as the Leo Triplet, the three magnificent galaxies gather in one field of view. Crowd pleasers when imaged with even modest telescopes, they can be introduced individually as NGC 3628 (left), M66 (bottom right), and M65 (top). All three are large spiral galaxies but they tend to look dissimilar because their galactic disks are tilted at different angles to our line of sight. NGC 3628 is seen edge-on, with obscuring dust lanes cutting across the plane of the galaxy, while the disks of M66 and M65 are both inclined enough to show off their spiral structure. Gravitational interactions between galaxies in the group have also left telltale signs, including the warped and inflated disk of NGC 3628 and the drawn out spiral arms of M66. This gorgeous view of the region spans about one degree (two full moons) on the sky. The field covers over 500 thousand light-years at the trio's estimated distance of 30 million light-years.

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[heehaw]

When I was a boy looking at photos similar to this one (but black-and-white, and grainy) I saw MATTER in EMPTY SPACE. Now I see a small light-emitting fraction of all the baryonic matter that is really there, and I know that it is surrounded by much much greater amounts of dark matter (unknown physics!) and all that is on top of a uniform repulsive dark energy that is literally exploding our poor universe! What progress! And my own brain - I now have to type earth htrae each day, and then delete the earth! What a fate!

[Ann]

Nice picture, and a very interesting trio of galaxies.

Click to view full size image

NGC 3628. Photo: Jim Misti/Rob Gendler.

Let's start with the galaxy that Messier didn't spot, NGC 3628. Its shape is interesting not only because of the way the disk flares out at both ends, which is extremely unusual, but also because of the long, faint tidal tail that can just be seen in today's APOD. It appears to originate at the "bottom end" of the disk in the APOD and curve down and slightly to the left.

Another interesting aspect of edge-on NGC 3628 is that its luminous disk appears to be very "long", and therefore larger in size than M65 and M66. If we saw it face on, it would be larger than either of the Messier galaxies. Note however that its yellow inner disk is smaller in size than the yellow inner disk of M65, which is very obvious in today's APOD. And indeed, NGC 3628 has a bluer B-V index than M65, 0.800 versus 0.920. On the other hand, NGC 3628 seems to contain very little star formation. Note the sharp peanut shape of its inner bulge, which strongly suggests that NGC 3628 has a central bar.

Click to view full size image

M65. Chuck Greenberg & Scott Tucker/Adam Block/AURA/NOAO/NSF

The yellowest of the galaxies of the Leo trio of M65, a well-formed and elegant galaxy of Hubble type SBb. The galaxy is dominated by a yellow disk, a ring and a bar. There is extremely little star formation in M65, but note some blue-white clumps in the upper right part of the ring, which are clusters of young stars. And fascinatingly, for a galaxy with so little star formation, a massive young star close to these young clusters in M65 went supernova in 2013! It was a core-collapse supernova, SN 2013 am. The picture is by Bill Snyder.

Click to view full size image

M66. Photo: Velimir Popov/ELATE Observatory.

The galaxy with the largest amount of star formation of the Leo trio is undoubtedly M66. However, all the star formation appears to take part in the inner disk, and its large outer disk (or broad tidal tails?) are dominated by old yellow stars. This is not unusual. Star formation is quenched in the central part of many galaxies but goes on in the outer parts, but there are several examples of the opposite, too. NGC 4314 is a galaxy where a lot of star formaiton is taking place in s small inner ring near the nucleus, but no new stars are born anywhere else in the galaxy.

Note the twisted shape of M66.

Ann

[tomatoherd]

Heehaw:
I bet as a child you also read the story of the Emperor's new clothes. Well they were woven out of dark matter, BTW.

[neufer]

When I was a boy looking at photos similar to this one (but black-and-white, and grainy) I saw MATTER in EMPTY SPACE. Now I see a small light-emitting fraction of all the baryonic matter that is really there, and I know that it is surrounded by much much greater amounts of dark matter (unknown physics!) and all that is on top of a uniform repulsive dark energy that is literally exploding our poor universe!

I bet as a child you also read the story of the Emperor's new clothes. Well they were woven out of dark matter, BTW.

<<The spiral of silence theory stipulates that individuals have a fear of isolation, which results from the idea that a social group or the society in general might isolate, neglect, or exclude members due to the members' opinions. This fear of isolation consequently leads to remaining silent instead of voicing opinions. The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak.">>

<<Lord Kelvin estimated the number of dark bodies in the Milky Way galaxy from the observed velocity dispersion of the stars, the speed the stars were orbiting around the center of the galaxy, which he used to estimate the mass of the galaxy, which was different than the mass of stars which can be seen, and concluded that “many of our stars, perhaps a great majority of them, may be dark bodies.” In 1906 Henri Poincaré in the “The Milky Way and Theory of Gases” used "dark matter,” or “matière obscure” in French in discussing Kelvin's work.

In 1933, Swiss astrophysicist Fritz Zwicky applied the virial theorem to the Coma galaxy cluster and obtained evidence of unseen mass that he called dunkle Materie 'dark matter'. Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and number of galaxies. He estimated that the cluster had about 400 times more mass than was visually observable. Zwicky's estimates were off by more than an order of magnitude, mainly due to an obsolete value of the Hubble constant; the same calculation today shows a smaller fraction, using greater values for luminous mass.

The first robust indications that the mass to light ratio was anything other than unity came from measurements of galaxy rotation curves. In 1939, Horace W. Babcock reported the rotation curve for the Andromeda nebula, which suggested that the mass-to-luminosity ratio increases radially. He attributed it to either light absorption within the galaxy or modified dynamics in the outer portions of the spiral and not to missing matter.

Vera Rubin and Kent Ford in the 1960s–1970s provided further strong evidence, also using galaxy rotation curves. Rubin worked with a new spectrograph to measure the velocity curve of edge-on spiral galaxies with greater accuracy. An influential paper presented Rubin's results in 1980. Rubin found that most galaxies must contain about six times as much dark as visible mass; thus, by around 1980 the apparent need for dark matter was widely recognized as a major unsolved problem in astronomy.>>

[tomatoherd]

Thanks, Art for the info.
I certainly don't fear isolation, and am usually TOO ready to share my opinion.
Speaking out of ignorance, one thing I don't get it how anyone can figure momentum anyway, since there is no observable OR MEASURABLE motion of a galaxy over a human lifetime. So how the h@ll can they tell how fast they are rotating, and hence how much matter is involved? Isn't it all conjecture?
Meanwhile, Pshaw on dark matter. It'll all be changed again in a couple generations, if we survive.

[Chris Peterson]

Speaking out of ignorance, one thing I don't get it how anyone can figure momentum anyway, since there is no observable OR MEASURABLE motion of a galaxy over a human lifetime. So how the h@ll can they tell how fast they are rotating, and hence how much matter is involved?

We can tell with high accuracy how fast nearly any luminous object is moving radially with respect to us by looking at its Doppler shift. The only galaxies that we can't measure this way are those which are almost perfectly face on, of which there are nearly none. This also lets us determine the direction a galaxy is turning, which isn't always the same as you'd assume from the direction of its spiral arms.

[tomatoherd]

So...there's a doppler shift on the side of the galaxy moving away from us and a blue shift on side towards us? And a big enough difference to measure? why have there been no APODs showing that? Is it so tiny it's not a visually demonstrable thing for a photo-based site? Is is just mathematical figures???

[Chris Peterson]

So...there's a doppler shift on the side of the galaxy moving away from us and a blue shift on side towards us?

Yes.

And a big enough difference to measure? why have there been no APODs showing that? Is it so tiny it's not a visually demonstrable thing for a photo-based site? Is is just mathematical figures???

Nothing moves fast enough for its Doppler shift to result in a visible shift of color. But it's trivially measured spectroscopically, even at very low speeds. For instance, the Sun takes about 25 days to make a complete rotation, but we can measure the red and blue shift on opposite sides of it. Here's a typical galaxy spectrum, showing the red and blue shifted hydrogen line:


This also shows the nearly constant speed which was the first indicator that there was much more mass around galaxies than is apparent from the luminous matter.

[tomatoherd]

Nothing moves fast enough for its Doppler shift to result in a visible shift of color.

sure it does. all those distant background galaxies are red! But i know what you mean, and appreciate the info and visuals. Seems like an APOD would have educated me already; the spectrographs (?) are certainly visual and interesting.

[tomatoherd]

Chris:
and by "constant" you mean radially constant, with the periphery moving almost as fast as the inner matter, unlike our solar system???

[sillyworm]

If we calculated the positions of these 3 Galaxies if we could view them as they would appear today(in their location)...how close would they be now? Would they be in the process of merging?

[Chris Peterson]

Nothing moves fast enough for its Doppler shift to result in a visible shift of color.

sure it does. all those distant background galaxies are red! But i know what you mean, and appreciate the info and visuals. Seems like an APOD would have educated me already; the spectrographs (?) are certainly visual and interesting.

Distant background galaxies are not Doppler shifted. The redshift we see in that case is cosmological redshift, caused by the stretching out of the wavelength as the photons travel through expanding spacetime.

[Chris Peterson]

Chris:
and by "constant" you mean radially constant, with the periphery moving almost as fast as the inner matter, unlike our solar system???

Yes.

[Chris Peterson]

If we calculated the positions of these 3 Galaxies if we could view them as they would appear today(in their location)...how close would they be now? Would they be in the process of merging?

They will not have changed position much in just 30 million years. The three are in complex orbits around each other, which could continue for billions of years without any collisions. Eventually, one of them will have its orbit perturbed by the others in a way that results in a collision. But even collisions don't necessarily produce complete mergers.

[tomatoherd]

Chris:
and by "constant" you mean radially constant, with the periphery moving almost as fast as the inner matter, unlike our solar system???

Yes.

So in other words, moving in a non-Keplerian, non-Newtonian way for the observed visible, calculated mass, hence the "necessity" for unseen mass, aka dark matter. correct?

(covering old ground, i'm sure)

[Chris Peterson]

Chris:
and by "constant" you mean radially constant, with the periphery moving almost as fast as the inner matter, unlike our solar system???

Yes.

So in other words, moving in a non-Keplerian, non-Newtonian way for the observed visible, calculated mass, hence the "necessity" for unseen mass, aka dark matter. correct?

(covering old ground, i'm sure)

Correct. So the more obvious possibilities are Keplerian orbit theory is wrong (unlikely), Newtonian gravity is wrong (unlikely), GR is wrong (unlikely in this particular), or there's simply more mass present than we can see. The latter seemed (and seems) most likely given the available pool of evidence, and this has only become more so as we see evidence of unseen mass in other observations, as well (such as gravitational lenses and the motion of galaxies in clusters).

[BDanielMayfield]

<<The spiral of silence theory stipulates that individuals have a fear of isolation, which results from the idea that a social group or the society in general might isolate, neglect, or exclude members due to the members' opinions. This fear of isolation consequently leads to remaining silent instead of voicing opinions. The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak.">>

I'm glad I didn't fall into that spiral. If no one ever dares to raise minority opinions discussion wanes and interest fades. Also, advancement can be stalled. Remember, haven't all current majority views started out as minority ideas?

Bruce, (an exception to the rule?)

[Chris Peterson]

<<The spiral of silence theory stipulates that individuals have a fear of isolation, which results from the idea that a social group or the society in general might isolate, neglect, or exclude members due to the members' opinions. This fear of isolation consequently leads to remaining silent instead of voicing opinions. The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak.">>

I'm glad I didn't fall into that spiral. If no one ever dares to raise minority opinions discussion wanes and interest fades. Also, advancement can be stalled. Remember, haven't all current majority views started out as minority ideas?

The distinction in science is that we reasonably expect those with minority views to actually be qualified to have those views.

[tomatoherd]

Actually, in hindsight, it was dark energy propelling the Emperor to walk faster and faster across the town square.

Flat-earth Tomatoherd.

[tomatoherd]

You scientists have it easy. Dissenting opinion only causes you brief dismay, such as by trolls like me. Then the tower is re-secured and snug.
But in the social sciences, politics, religion, even art, those with views which are incorrect (or bizarre, or degrading) are often those in authority, causing great worldwide havoc, and those with correct views are increasingly losing the battle to undo that harm. So take heart.

[Guest]

If no one ever dares to raise minority opinions discussion wanes and interest fades. Also, advancement can be stalled. Remember, haven't all current majority views started out as minority ideas?

The distinction in science is that we reasonably expect those with minority views to actually be qualified to have those views.

Classic deflection. Ignore the argument (especially if it's true), just assail the qualifications of the one making the argument.

For the record, I think the majority of astronomical consensus thinking is on the right track. And, being a non-scientist, I admit that I lack the skills to debate points in doubt on a deep level. However, it cannot be denied that more data sometimes alters thinking and forces old theories to be discarded. The Steady State theory being replaced by the Big Bang is a prime example. Therefore I think being overly locked in to a "this is what the majority think, so no contrary ideas will be tolerated at all" mindset can impede progress.

Bruce

[Chris Peterson]

If no one ever dares to raise minority opinions discussion wanes and interest fades. Also, advancement can be stalled. Remember, haven't all current majority views started out as minority ideas?

The distinction in science is that we reasonably expect those with minority views to actually be qualified to have those views.

Classic deflection. Ignore the argument (especially if it's true), just assail the qualifications of the one making the argument.

No. Appeal to authority is only a fallacy when the authority has no authority. A person qualified to have a non-mainstream view about some aspect of science where there actually is a consensus will almost certainly be an active researcher with a peer-reviewed publication history in that subject.

[BDanielMayfield]

The distinction in science is that we reasonably expect those with minority views to actually be qualified to have those views.

Classic deflection. Ignore the argument (especially if it's true), just assail the qualifications of the one making the argument.

No. Appeal to authority is only a fallacy when the authority has no authority. A person qualified to have a non-mainstream view about some aspect of science where there actually is a consensus will almost certainly be an active researcher with a peer-reviewed publication history in that subject.

Note that in this exchange I haven't even brought up any particular non-mainstream view, I've merely dared to point out that mainstream views are subject to change as new data comes in. The mainstream view once was that everything revolved around the Earth; the invention of the telescope proved that wasn't the case. New tools could alter understandings in the future as well. One doesn't need to be a rocket (or any other type of) scientist to hold this valid opinion.

Bruce

[neufer]

<<The spiral of silence theory stipulates that individuals have a fear of isolation, which results from the idea that a social group or the society in general might isolate, neglect, or exclude members due to the members' opinions. This fear of isolation consequently leads to remaining silent instead of voicing opinions. The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak.">>

I'm glad I didn't fall into that spiral. If no one ever dares to raise minority opinions discussion wanes and interest fades. Also, advancement can be stalled. Remember, haven't all current majority views started out as minority ideas?

• “There are three stages of scientific discovery:
  • first people deny it is true;
    then they deny it is important;
    finally they credit the wrong person.”

---

<<James Croll (2 January 1821 – 15 December 1890) was born in 1821 on the farm of Little Whitefield in Perthshire, Scotland. He was largely self-educated. In 1859, he became a janitor at the museum of the Andersonian University in Glasgow. He was able to use the university library to get access to books, and taught himself physics and astronomy to develop his ideas.

From 1864, Croll corresponded with Sir Charles Lyell, on links between ice ages and variations in the Earth's orbit. This led to a position in the Edinburgh office of the Geological Survey of Scotland, as keeper of maps and correspondence, where the director, Sir Archibald Geikie, encouraged his research. He published a number of books and papers which "were at the forefront of contemporary science", including Climate and Time, in Their Geological Relations in 1875. He corresponded with Charles Darwin on erosion by rivers.

Croll was the leading proponent of an astronomical theory of climate change in the nineteenth century. Using formulae for orbital variations developed by Urbain Le Verrier (which had led to the discovery of Neptune), Croll developed a theory of the effects of variations of the Earth's orbit on climate cycles. His idea was that decreases in winter sunlight would favour snow accumulation, and for the first time coupled this to the idea of a positive ice-albedo feedback to amplify the solar variations. Croll further argued that the accumulation of snow would change the pattern of trade winds, leading to the deflection of warming currents like the Gulf Stream, and finally a self-sustaining ice age. He suggested that when orbital eccentricity is high, then winters will tend to be colder when the Earth is farther from the sun in that season and hence, that during periods of high orbital eccentricity, ice ages occur on 22,000-year cycles in each hemisphere, and alternate between southern and northern hemispheres, lasting approximately 10,000 years each.

Croll's theory predicted multiple ice ages, asynchronous in northern and southern hemispheres, and that the last ice ages should have ended about 80,000 years ago. Evidence was just then emerging of multiple ice ages, and geologists were interested in a theory to explain this. Geologists were not then able to date sediments accurately enough to determine if glaciation was synchronous between the hemispheres, though the limited evidence more pointed towards synchronicity than not. More crucially, estimates of the recession rate of the Niagara Falls indicated that the last ice age ended 6,000 to 35,000 years ago – a large range, but enough to rule out Croll's theory, to those who accepted the measurements.

Croll's work was widely discussed, but by the end of the 19th century, his theory was generally disbelieved. However, the basic idea of orbitally-forced insolation variations influencing terrestrial temperatures – now known generally as Milankovitch cycles – was further developed by the Serbian civil engineer Milutin Milankovitch (28 May 1879 – 12 December 1958) and eventually, in modified form, triumphed in 1976.>>