APOD: NGC 4651: The Umbrella Galaxy (2014 Jul 02)

[APOD Robot]

NGC 4651: The Umbrella Galaxy

Explanation: Spiral galaxy NGC 4651 is a mere 62 million light-years distant, toward the well-groomed northern constellation Coma Berenices. About the size of our Milky Way, this island universe is seen to have a faint umbrella-shaped structure that seems to extend (left) some 100 thousand light-years beyond the bright galactic disk. The giant cosmic umbrella is now known to be composed of tidal star streams - extensive trails of stars gravitationally stripped from a smaller satellite galaxy. The small galaxy was eventually torn apart in repeated encounters as it swept back and forth on eccentric orbits through NGC 4651. In fact, the picture insert zooms in on the smaller galaxy's remnant core, identified in an extensive exploration of the system, using data from the large Subaru and Keck telescopes on Mauna Kea. Work begun by a remarkable collaboration of amateur and professional astronomers to image faint structures around bright galaxies suggests that even in nearby galaxies, tidal star streams are common markers of such galactic mergers. The result is explained by models of galaxy formation that also apply to our own Milky Way.

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[bystander]

AAO: Distant 'Cannibal Twin' Shows How Galaxies Grow
Keck: Merging Galaxies Illuminate the Cosmic Food Chain
Stellar Steam and Progenitor Satellite Nucleus in NGC 4651

[rick357]

The background is truly humbling. There are galaxies everywhere. I wonder if this is an example of a galaxy cluster, a view edge-on down one of the walls, or a bit of both?

[Chris Peterson]

The background is truly humbling. There are galaxies everywhere. I wonder if this is an example of a galaxy cluster, a view edge-on down one of the walls, or a bit of both?

I think there's nothing special at all. Look deeply at any bit of the sky only a few arcminutes across and you'll see a background of galaxies (and very few stars if you're not looking through the disc of the Milky Way).

[NGC3314]

There may be a background cluster of galaxies south of the small galaxy remnant - one of the blue objects is the quasar 3C 275.1 at z=0.55. An SDSS finding chart centered on the quasar is here. Some of those galaxies look about the right color and magnitude to be in a cluster around the quasar. Poking around a bit, there is at least X-ray evidence for a surrounding cluster. Unfortunately there are no Sloan survey spectra for other possible members. NED lists 3 galaxies at closely matching redshifts within 90 arcseconds (among many others at a wide range of distance).

Looking at an old image of mine, I do wonder whether the contrast compression needed for display to avoid saturation of the galaxy or losing the tidal features might make background galaxies more or less prominent in different parts of the field.

[hlwelborn]

What does the term "island universe" mean?

[geckzilla]

What does the term "island universe" mean?

It's a throwback to the days when people thought the Milky Way was the whole universe. Once it was hypothesized that spiral nebulas thought to be within our galaxy are actually distant, other Milky Ways, it made sense to call them that before transitioning our concept of the universe to a much larger scale.

[BrentH]

I have a question: Why is it that the arms of all spiral galaxies go in one direction? (from the center they swing out in a clockwise direction). It would seem that, even if this was a law of nature, that we would be looking at half the galaxies in the universe from the underside and thus se them spiraling in the other direction, but this seems to never be true. Why is that?

[geckzilla]

I have a question: Why is it that the arms of all spiral galaxies go in one direction?

They don't...

Edit: Dramatic example.
http://apod.nasa.gov/apod/ap090407.html

[BMAONE23]

What does the term "island universe" mean?

It's a throwback to the days when people thought the Milky Way was the whole universe. Once it was hypothesized that spiral nebulas thought to be within our galaxy are actually distant, other Milky Ways, it made sense to call them that before transitioning our concept of the universe to a much larger scale.

I think that the term "Island Universe" is a good term and makes a valid analogy though. Although the Galaxy is much smaller than and part of the known visible universe, our current technology makes it impossible for any individual to get to even our next closest neighboring star.

Our current tech allows us to travel at close enough to 1 LY every 10,000 years to use this ratio for comparative purposes.
Alpha Centauri is 4.2ly away and would take over 42000 years to get there. The MW is 100,000ly across and would take 1,000,000,000 (1 billion) years to cross. Andromeda is 2.2M LY away and would take 22,000,000,000 (22 billion) years to reach.

Since we can't travel to them without some sort of technology or understanding of physics that allows for Faster than Light travel, each galaxy is basically a Self-Contained universe for all practical purposes

[starsurfer]

My prediction for the future from yesterday was correct! It's interesting that these tidal tails were first identified in the 1950's. I hope Jay GaBany releases more of the tidal stream survey results, I've been anticipating NGC 1084 for quite a few years now.

[Ron-Astro Pharmacist]

The remnant core is one of the interesting features in today's APOD. They would seem to be pretty unique objects but don't ever remember reading of them before. If our galaxy has had previous collisions where would the remnant core reside following the interaction?

http://www.gresham.ac.uk/lectures-and-e ... es-collide

Professor Carolin Crawford gives a great lecture on galaxies and their collisions.

[aglaia]

My wife looked at the umbrella galaxy this morning, and immediately called it the lollipop galaxy.

[LocalColor]

The remnant core is one of the interesting features in today's APOD. They would seem to be pretty unique objects but don't ever remember reading of them before. If our galaxy has had previous collisions where would the remnant core reside following the interaction?

http://www.gresham.ac.uk/lectures-and-e ... es-collide

Professor Carolin Crawford gives a great lecture on galaxies and their collisions.

Thank you - this will be our "dinner lecture" this evening.

[Boomer12k]

Can someone explain WHY the larger galaxy still has allot of "structure" to it...while the other is basically obliterated????

Is it because of the MASS??? Like a small car and a Large Truck???

Very nice, and interesting picture.

:---[===] *

[Boomer12k]

There APPEARS...at least to me....that there is some slight GALACTIC LENSING on the left side where the majority of the demolished galaxy is....between the crescent inward.


The background seems to be more SQUISHED together there....

OR maybe it is a COMPOSITE PICTURE from the various places, and those areas were actually done with higher magnification???

:---[===] *

[Cousin Ricky]

Why is the remnant galaxy core blue in color?

[starsurfer]

Why is the remnant galaxy core blue in color?

I think that might be an illusion as we see it through the blue tidal tail.

[Chris Peterson]

There APPEARS...at least to me....that there is some slight GALACTIC LENSING on the left side where the majority of the demolished galaxy is....between the crescent inward.

The background seems to be more SQUISHED together there...

No. This galaxy is too close and too extended to produce any sort of visible lensing. Furthermore, lensing would not produce a distorted star field.

OR maybe it is a COMPOSITE PICTURE from the various places, and those areas were actually done with higher magnification?

No, there's nothing to suggest the image isn't dimensionally accurate.

[Chris Peterson]

Why is the remnant galaxy core blue in color?

Given the source images and the method of creating color, I'd be skeptical that what we're seeing is necessarily all that accurate (in terms of color). Also, a huge amount of contrast stretching or layer compositing had to be utilized to bring out the tidal tail, which in reality is many orders of magnitude dimmer than the galaxy. That means that any objects that overlap the tidal tail are more likely to show distorted color, as well.

[Ann]

Why is the remnant galaxy core blue in color?

Given the source images and the method of creating color, I'd be skeptical that what we're seeing is necessarily all that accurate (in terms of color). Also, a huge amount of contrast stretching or layer compositing had to be utilized to bring out the tidal tail, which in reality is many orders of magnitude dimmer than the galaxy. That means that any objects that overlap the tidal tail are more likely to show distorted color, as well.

I agree with Chris that the processing that was necessary to bring out this (bluish) tail has likely given objects seen in the tail a bluish tinge as well. Note the ring galaxy seen next to the remnant galaxy core. While it isn't blue, it is less orange than many other background galaxies in this picture.

That said, I would guess that the remnant core of the dwarf galaxy really is - if not blue, then also not yellow. Consider Omega Centauri, which is indeed believed to be the remnant core of a shredded dwarf galaxy. This Hubble image of the center of Omega Centauri shows many blue stars there. Yes, the colors are exaggerated, but the blue (or bluish) stars are real. In Omega Centauri, the blue stars make a significant contribution to the overall light and color of this cluster. In the bulge of the Milky Way, the blue stars are extremely few and contribute very little light. It is likely that the bulge of NGC 4651 resembles the core of the Milky Way when it comes to color and stellar populations. If so, the bulge of NGC 4651 really should look yellow, whereas the core of the shredded dwarf galaxy should look non-yellow.

Ann

[starsurfer]

Also it mixes data from lots of different filters, which might not necessarily produce "truthful" colours as the main emphasis is revealing faint detail.