Starship Asterisk*

[img]https://apod.nasa.gov/apod/calendar/S_170421.jpg[/img] NGC 4302 and NGC 4298

Explanation: Seen edge-on, spiral galaxy NGC 4302 (left) lies about 55 million light-years away in the well-groomed constellation Coma Berenices. A member of the large Virgo Galaxy Cluster, it spans some 87,000 light-years, a little smaller than our own Milky Way. Like the Milky Way, NGC 4302's prominent dust lanes cut along the center of the galactic plane, obscuring and reddening the starlight from our perspective. Smaller companion galaxy NGC 4298 is also a dusty spiral. But tilted more nearly face-on to our view, NGC 4298 can show off dust lanes along spiral arms traced by the bluish light of young stars, as well as its bright yellowish core. In celebration of the 27th anniversary of the launch of the Hubble Space Telescope on April 24, 1990, astronomers used the legendary telescope to take this gorgeous visible light portrait of the contrasting galaxy pair.

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Very pretty.

How far apart might they be ?
Far enough that they appear to be not interacting with each other ?

If only there was some way to get both these viewpoints of the same galaxy.
But that may remain wishful thinking, for quite some time....

This is an interesting pair, but I really, really wish that the caption had provided a link to some technical data about the image. What I want to know most of all, of course, is what filters were used for the image. It doesn't look like an RGB picture to me.

There are a few things we can say, however. Like RocketRon pointed out, there are few signs of interaction between NGC 4302 and 4298. Edge-on NGC 4302 looks completely undisturbed, but there are perhaps signs of some tidal stretchings of the disk of NGC 4298.

Note that NGC 4302 doesn't bulge. It is perfectly flat. But it is (slightly) yellower in the middle than at the edges of its disk.

Neither of the galaxies appear to contain very much star formation. To get a better idea of the stellar content of the two galaxies, I searched for other pictures of them on the net and found this SDSSS one, which I quite like. A word of warning, though - I have not been able to find out how big the picture is.

It is interesting that both NGC 4302 and 4298 are smaller than the Milky Way. Very many galaxies seem to be smaller than the Milky Way, and relatively few seem to be bigger. I'm beginning to think that we live inside a quite big galaxy, where we orbit a quite big and massive Sun.

Ann

Striking!!!

Well, if they are a "dancing pair", they won't be "small" for too much longer...."cosmic time" scale speaking....

Well done.
:---[===] *

Ann, click on the "Fast Facts" link at:
http://hubblesite.org/image/4019/gallery

F475W (B), F555W (V), and F625W (r)

Nitpicker wrote:Ann, click on the "Fast Facts" link at:
http://hubblesite.org/image/4019/gallery

F475W (B), F555W (V), and F625W (r)

Thanks, but the filter info there isn't very good, IMO:

The Hubble observations were taken between January 2 and January 22, 2017 with the Wide Field Camera 3 (WFC3) instrument in three visible light bands.

Ann

Speaking of pizzas are these thin crust or deep dish galaxies?

I echo the earlier question. How far apart are these guys? Visual alignment looks less than 100K light years. Such proximity might suggest more tidal interaction unless they have just arrived at this distance for the first time. What a view from a planet located in either system! This also brings up the thought of when would the Milky Way begin to feel the tidal pull of Andromeda before the big smash happens?

Ann wrote:

Nitpicker wrote:Ann, click on the "Fast Facts" link at:
http://hubblesite.org/image/4019/gallery

F475W (B), F555W (V), and F625W (r)

Thanks, but the filter info there isn't very good, IMO:

The Hubble observations were taken between January 2 and January 22, 2017 with the Wide Field Camera 3 (WFC3) instrument in three visible light bands.

How so? Literally from that link,

Blue: F475W (B)
Green: F555W (V)
Red: F625W (r)

How much better can the information be?

Wow!

The caption for the picture says that NGC 4298 is a "smaller companion" of NGC 4302, which I would assume means it lies at roughly the same distance of 55 million light-years. But if that's so, I'd expect to see a lot more interaction than just some tidal stretching of NGC 4298. Is it possible the distance estimate is incorrect for NGC 4298?

Fred the Cat wrote:Speaking of pizzas are these thin crust or deep dish galaxies?

Not to “carry this out” too far but the pizza to galaxy analogy works well. As soon you have the makings you start spinning the dough. There are all sorts of toppings the can have; some old and gnarly like a globular sausage and some fresh and hot like a triple habanero star.

And they were all created long ago in the biggest pizza oven. A dark matter rim keeps the outside spinning as fast as the center and dark energy was created like a rebounding trampoline when our universe was created. This astrophysics stuff is as easy as pie.

Doesn't it matter that what is being observed happened 55 million years ago? Without subsequent data, what is the validity of present day conjecture?

DLMartin wrote:Doesn't it matter that what is being observed happened 55 million years ago? Without subsequent data, what is the validity of present day conjecture?

It is completely irrelevant. For any practical purpose, it is happening as we observe it.

sytheblackwolfe wrote:The caption for the picture says that NGC 4298 is a "smaller companion" of NGC 4302, which I would assume means it lies at roughly the same distance of 55 million light-years. But if that's so, I'd expect to see a lot more interaction than just some tidal stretching of NGC 4298. Is it possible the distance estimate is incorrect for NGC 4298?

I would not assume "smaller" means physically smaller, but rather, apparently smaller.

Large astronomical distances are difficult to determine. The distance to these objects is only known to about a 20% error range. Either one could be one or two million light years farther away than the other and we'd have no clear way of telling that. In other words, they could easily be as far apart as the Milky Way and Andromeda, which have very little tidal interaction.

Thank you for the clear explanation, Chris! It makes a lot more sense now.

RocketRon wrote:Very pretty.

How far apart might they be?

Ann wrote:Like RocketRon pointed out, there are few signs of interaction between NGC 4302 and 4298. Edge-on NGC 4302 looks completely undisturbed, but there are perhaps signs of some tidal stretchings of the disk of NGC 4298.

NCTom wrote:I echo the earlier question. How far apart are these guys? Visual alignment looks less than 100K light years. Such proximity might suggest more tidal interaction unless they have just arrived at this distance for the first time.

Is there a way to tell how far away from each other they are in the depth dimension? Since these two galaxies show little to no tidal stretching yet I'd surmise that they could really be much farther apart than they appear. Is there even any way to be sure which of these two is in front of the other?

NCTom, if they actually where as close as they look I think there would have to be way more signs of distortion than what they show.

Bruce

BDanielMayfield wrote:Is there a way to tell how far away from each other they are in the depth dimension? Since these two galaxies show little to no tidal stretching yet I'd surmise that they could really be much farther apart than they appear. Is there even any way to be sure which of these two is in front of the other?

One possibility would be to very accurately measure the redshift of each. They are almost certainly a gravitationally bound pair, and will therefore have virtually identical cosmological redshifts. That means that any difference would represent a Doppler shift, which would provide information about the relative motion between the two along our line of sight. That's not enough to fully determine their orbits, but it could be enough to feed a model and arrive at a set of likely orbits, and therefore some idea about their actual separation.

BDanielMayfield wrote:
Is there a way to tell how far away from each other they are in the depth dimension? Since these two galaxies show little to no tidal stretching yet I'd surmise that they could really be much farther apart than they appear. Is there even any way to be sure which of these two is in front of the other?

• They are both part of the Virgo Cluster which is 2.2 Mpc in radius.
  
  Since there is "little to no tidal stretching" it would seem reasonable to assume
  that they are probably about 2 Mpc apart(; i.e., at 15.5 & 17.5 Mpc, respectively).

https://en.wikipedia.org/wiki/Virgo_Cluster wrote:
<<The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo. Comprising approximately 1300 (and possibly up to 2000) member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group is an outlying member. However, the Local Group experiences the mass of the Virgo Supercluster as the Virgocentric flow. It is estimated that the Virgo Cluster's mass is 1.2×10¹⁵M_☉ out to 8 degrees of the cluster's center or a radius of about 2.2 Mpc.

The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Many of the member galaxies of the cluster are visible with a small telescope. Its brightest member is the elliptical galaxy Messier 49; however its most famous member is the also elliptical galaxy Messier 87, that unlike the former is located in the center of the cluster.>>

Chris Peterson wrote:

Ann wrote:

Nitpicker wrote:Ann, click on the "Fast Facts" link at:
http://hubblesite.org/image/4019/gallery

Thanks, but the filter info there isn't very good, IMO:

The Hubble observations were taken between January 2 and January 22, 2017 with the Wide Field Camera 3 (WFC3) instrument in three visible light bands.

How so? Literally from that link,

Blue: F475W (B)
Green: F555W (V)
Red: F625W (r)

How much better can the information be?

Thanks, Chris! For some reason, I couldn't see that information.

Ann

Chris Peterson wrote:

sytheblackwolfe wrote:The caption for the picture says that NGC 4298 is a "smaller companion" of NGC 4302, which I would assume means it lies at roughly the same distance of 55 million light-years. But if that's so, I'd expect to see a lot more interaction than just some tidal stretching of NGC 4298. Is it possible the distance estimate is incorrect for NGC 4298?

I would not assume "smaller" means physically smaller, but rather, apparently smaller.

Large astronomical distances are difficult to determine. The distance to these objects is only known to about a 20% error range. Either one could be one or two million light years farther away than the other and we'd have no clear way of telling that. In other words, they could easily be as far apart as the Milky Way and Andromeda, which have very little tidal interaction.

I would, in fact, guess that NGC 4302 is indeed physically bigger than NGC 4298. Even though these galaxies might well be separated by 2 million light years or so, at a distance of ~55 million light-years that wouldn't affect the apparent size of them all that much. Indeed, such a separation could enhance the apparent difference in size, but I don't think it could create it from scratch if these two galaxies were indeed the same size. NGC 4302 does appear to have a more extensive disk. Also NGC 4302 appears yellower than NGC 4298. Yes, edge-on galaxies typically appear yellower than face-on ones, because the dust lane itself imparts reddening, but in the case of NGC 4302 it definitely has a yellow inner disk. Larger galaxies are expected to have produced a larger yellow population than smaller galaxies.

So I would think that NGC 4302 is bigger than NGC 4298, but I also think that these galaxies are separated by a sufficiently large distance that they don't cause much tidal stretching of each other's disks.

Ann

Ann wrote:

Chris Peterson wrote:

sytheblackwolfe wrote:The caption for the picture says that NGC 4298 is a "smaller companion" of NGC 4302, which I would assume means it lies at roughly the same distance of 55 million light-years. But if that's so, I'd expect to see a lot more interaction than just some tidal stretching of NGC 4298. Is it possible the distance estimate is incorrect for NGC 4298?

I would not assume "smaller" means physically smaller, but rather, apparently smaller.

Large astronomical distances are difficult to determine. The distance to these objects is only known to about a 20% error range. Either one could be one or two million light years farther away than the other and we'd have no clear way of telling that. In other words, they could easily be as far apart as the Milky Way and Andromeda, which have very little tidal interaction.

I would, in fact, guess that NGC 4302 is indeed physically bigger than NGC 4298.

That would be my guess, as well. But I don't think that was the intent of the word usage in the caption.

Ann wrote:
I would, in fact, guess that NGC 4302 is indeed physically bigger than NGC 4298. Even though these galaxies might well be separated by 2 million light years or so, at a distance of ~55 million light-years that wouldn't affect the apparent size of them all that much. Indeed, such a separation could enhance the apparent difference in size, but I don't think it could create it from scratch if these two galaxies were indeed the same size. NGC 4302 does appear to have a more extensive disk. Also NGC 4302 appears yellower than NGC 4298. Yes, edge-on galaxies typically appear yellower than face-on ones, because the dust lane itself imparts reddening, but in the case of NGC 4302 it definitely has a yellow inner disk. Larger galaxies are expected to have produced a larger yellow population than smaller galaxies.

So I would think that NGC 4302 is bigger than NGC 4298, but I also think that these galaxies are separated by a sufficiently large distance that they don't cause much tidal stretching of each other's disks.

http://asterisk.apod.com/viewtopic.php?f=9&t=37102#p269784 wrote:
Since there is "little to no tidal stretching" it would seem reasonable to assume
that they are probably about 2 Mpc apart(; i.e., at 15.5 & 17.5 Mpc, respectively).

The limited size of the Virgo cluster means that they can't possibly be separated by more than 4.4 Mpc (; i.e., at ~14.3 & ~18.7 Mpc, respectively) in which case NGC 4298 would appear be 30% larger if they were placed at the same distance.

However, NGC 4302 apparent length is well over 80% longer than NGC 4298.

The late Alan Sandage of cosmology fame was at Johns Hopkins briefly about the time he published his
https://www.amazon.com/Hubble-Atlas-Gal ... 0872796299
Please don't buy this Atlas: it is incredibly antique, with black-and-white photos of galaxies. How things have changed!
Alan engaged in a HUGE battle over the value of the Hubble parameter: Alan argued for (hold your breath) 42, while De Vaucouleurs argued for 100. There was an historic debate in DC, not between those two, who despised each other, but between stand-ins (for De Vaucouleurs, my Masters thesis advisor, Sidney van den Bergh, and for Alan, Gustav Tamman). It was a draw (I was there). Of course the current value is about half way between the two, but slightly closer to Alan's value I guess. I was enjoying drinks at a table in Italy when Alan invited Gus to join him in California....

I Googled NGC 4302 and NGC 4298 and the first hit that wasn't this Apod page or a youtube page that zoomed in on the Hubble Image, was the Deep Sky Object Search. According to them the distance of NGC 4302 is 53 M light years, and the distance of NGC 4298 is 52 M light years. So NGC 4298 is 1 M light years in front of 4302 and therefore closer to us making it truly smaller than its companion.