APOD: Comet ATLAS and the Mighty Galaxies (2020 Mar 21)

[APOD Robot]

Comet ATLAS and the Mighty Galaxies

Explanation: Comet ATLAS C/2019 Y4 was discovered by the NASA funded Asteroid Terrestrial-impact Last Alert System, the last comet discovery reported in 2019. Now growing brighter in northern night skies, the comet's pretty greenish coma is at the upper left of this telescopic skyview captured from a remotely operated observatory in New Mexico on March 18. At lower right are M81 and M82, well-known as large, gravitationally interacting galaxies. Seen through faint dust clouds above the Milky Way, the galaxy pair lies about 12 million light-years distant, toward the constellation Ursa Major. In bound Comet ATLAS is about 9 light-minutes from Earth, still beyond the orbit of Mars. The comet's elongated orbit is similar to orbit of the Great Comet of 1844 though, a trajectory that will return this comet to the inner Solar System in about 6,000 years. Comet ATLAS will reach a perihelion or closest approach to the Sun on May 31 inside the orbit of Mercury and may become a naked-eye comet in the coming days.

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[Ann]

Today's APOD is a very nice picture!

Comet ATLAS and the Mighty Galaxies. From top left to bottom right, Comet ATLAS, yellow-colored star HD 83126, galaxy NGC 2976, and well-known galaxies M81 and M82. Image Credit & Copyright: Rolando Ligustri (CARA Project, CAST)

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NGC 2976 is a dwarf galaxy classified as Irr and sometimes as Sc/P. NGC 2976 is a member of the M 81 group and is still connected to M 81 by a trail of dust and gas. Photo: Glen Youman.

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NGC 2976 is a weird little galaxy. I think someone called it "a spiral without spiral structure". You can see in Glen Youman's picture how the dusty and starforming part of the galaxy is surrounded by a large diffuse and purely stellar halo. I think we are seeing a galaxy that has lost a non-negligent amount of its gas reservoir, so that its inner dusty and gas-rich region has shrunk. This image by Sloan Digital Sky Survey shows the stellar halo of NGC 2976 reaching far beyond its dusty and starforming disk.

Runaway galaxy ESO 137-001 is speeding through the hot intracluster medium of the Norma Cluster of galaxies and leaving a long trail of gas behind. Photo: NASA, ESA, Hubble, Chandra X-ray Telescope.

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What has happened to NGC 2976? My guess is that it has passed too close to M81 and been stripped of some of its gas in the process.

Take a look at runaway galaxy ESO 137-001 at left, which is losing a dramatic amount of its own gas as it is speeding through the Norma Cluster of galaxies. NGC 2976 is certainly not losing that much gas, because it is a small galaxy with a limited reservoir of gas in the first place. But as Glen Youman pointed out on his web page, NGC 2976 is connected to much larger M81 through a trail of gas and dust.

So there may actually be "two comets" in today's APOD, not only Comet ATLAS but also "cometary galaxy" NGC 2976!

Click to view full size image

Comet ATLAS. Photo: NASA.

[orin stepanek]

ATLAS comes; I hope it is available for me to see as it approaches the sun! The only one I have seen was Hale Bopp! I may have seen others without knowing what they were!

[GeoXXX]

What a beautiful image. The “clouds” in the photo that give it such a dreamy quality is actually part of the Milky Way...

“ Most images of M81 and M82 will show the two galaxies, the surrounding stars and a few smaller galaxies here and there.

But a deeper exposure and a much more careful processing will reveal that these galaxies, far from being visualized against a nearly dark, empty background, they are surrounded by huge clouds of dust.

The truth is that the galaxies are not surrounded by this dust - the dust is much closer to us than the galaxies - it just happens to look that way. Kind of like looking at the moon on a partially cloudy night.

This dust, unlike classic reflection nebulas - that are usually illuminated by neighboring stars - is actually illuminated by the glow of our own Milky Way galaxy. And yes, it is very very faint. Steve Mandel named this nebulosity Integrated Flux Nebula, or IFN.”

https://www.spacetelescope.org/projects ... _andreo_1/

[neufer]

ATLAS comes; I hope it is available for me to see as it approaches the sun! The only one I have seen was Hale Bopp! I may have seen others without knowing what they were!

• Are you running out of gas, crumbling and fading as we speak

During January to March 2020, the comet is located in the constellation Ursa Major. On April when it gets dark it will be visible halfway up in the north-northwest sky and on June it will be visible on Orion constellation in the north-northeast sky at morning and potentially visible with the naked eye.

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Karl Battams of the Naval Research Lab in Washington DC said:

• "Comet ATLAS continues to be much brighter than expected. Some predictions for its peak brightness now border on the absurd. If it has a big nucleus with large stones of frozen gas, then yes; We could get a very bright Comet. Right now the Comet is releasing huge amounts of its frozen volatiles or gases. That's why it is brightening so fast, otherwise comet ATLAS might run out of gas, crumbling and fading as it approaches the Sun.
  
  Current best estimates of the comet peak brightness in May range from magnitude +1 to -5. If the comet hits the high end of that range, a bit brighter than Venus. Comet MC Naught or C/2006 P1 performed that very trick 13 years ago. On January 13, 2007, it swooped passed the sun shining at a brilliant magnitude of -5.5. The absurdly-bright comet was visible at high on noon with its tail jutting across the blue sky."

Battams is not optimistic, though, he added:

• "My personal intuition is that comet ATLAS is over archiving, and I wouldn't be surprised to see it fade rapidly and possibly even disintegrate before reaching the Sun. ATLAS is a bit of a wildcard, and there's a spectrum of possibilities as it nears the sun. At one extreme, it could simply crumble away in the coming weeks and at another extreme it could brighten up tremendously. It has an unusually small perihelion distance inside of Mercury's orbit, which bodes well for getting those frozen gasses fizzing furiously. If it can survive the blast furnace of the solar heating, it could put on a good show. However, no one expected the show to start more than two months before its perihelion. Comet ATLAS is already heating up. Outburst are possible in the upcoming weeks as new veins of volatile material are exposed by intensifying sunlight. The worldwide Comet Observation Database shows it jumping from magnitude +17 in early February to +8 in mid-March,4000 times brighter since its discovery. It could become visible to the naked eye in early April at this rate. If it doesn't fly apart first, it could become one of the brightest comets in years. However, the fate of the comet is still unclear. We do not know if it will ever return to our astronomical neighborhood again. He added, we have a number of space telescopes designed to view objects very close to sun. The Heliospheric Image on NASA's STEREO spacecraft will get a great view of it from mid-May through early June of 2020. So, we might be able to observe ATLAS's tail interacting with the Solar wind and outflows as well as any potentially breakup events. There's also WISPR camera on NASA's Parker Solar Probe. We will potentially be able to view ATLAS from WISPR camera concurrently with the STEREO observations. But it would require a non-standard pointing configuration for us, so the operation teams are currently assessing our options."

The comet has also been founded to be a hundred times bigger and brighter than what astronomers were originally estimating. By the time Comet ATLAS approaches the sun in late May it could become quite bright indeed. At present while in the vicinity of our neighbouring planet, ATLAS shines as an eighth magnitude fuzzy star, which is barely visible to the naked eye from any distant or remote location but can be observable through mid-sized backyard telescopes. Barely visible some three weeks ago, it has now surged in brightness and will continue to do so as it approaches the centre of our solar system. The comet has also been found to be hundreds of times bigger and brighter than what astronomers had originally estimated, possibly signaling an explosion or outburst of dust and gas in the comet's core or nucleus. If that continues to occur on its way to perihelion or if it brightens at a rate of 0.50 magnitude per day, which is double the current rate, then the comet may become the brightest comet in human history and be visible during daylight, which is very commonly seen for Kreutz sungrazer comets.>>

<<The Great Plague, lasting from 1665 to 1666, was the last major epidemic of the bubonic plague to occur in England. The Great Plague killed an estimated 100,000 people—almost a quarter of London's population—in 18 months. During the winter of 1664, a bright comet was to be seen in the sky and the people of London were fearful, wondering what evil event it portended:>>

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• ....................................................................
  • History of the Plague in London by Daniel Defoe
  A blazing star or comet appeared for several months before the plague, as there did, the year after, another a little before the fire. The old women, and the phlegmatic hypochondriac part of the other sex (whom I could almost call old women too), remarked, especially afterward, though not till both those judgments were over, that those two comets passed directly over the city, and that so very near the houses that it was plain they imported something peculiar to the city alone; that the comet before the pestilence was of a faint, dull, languid color, and its motion very heavy, solemn, and slow, but that the comet before the fire was bright and sparkling, or, as others said, flaming, and its motion swift and furious; and that, accordingly, one foretold a heavy judgment, slow but severe, terrible, and frightful, as was the plague, but the other foretold a stroke, sudden, swift, and fiery, as was the conflagration. Nay, so particular some people were, that, as they looked upon that comet preceding the fire, they fancied that they not only saw it pass swiftly and fiercely, and could perceive the motion with their eye, but even they heard it; that it made a rushing, mighty noise, fierce and terrible, though at a distance, and but just perceivable.
  
  I saw both these stars, and, I must confess, had had so much of the common notion of such things in my head, that I was apt to look upon them as the forerunners and warnings of God's judgments, and, especially when the plague had followed the first, I yet saw another of the like kind, I could not but say, God had not yet sufficiently scourged the city.

[orin stepanek]

ATLAS comes; I hope it is available for me to see as it approaches the sun! The only one I have seen was Hale Bopp! I may have seen others without knowing what they were!

• Are you running out of gas, crumbling and fading as we speak

When I was a little boy; I remember hoping for the return of Halley's Comet! turned out it didn't do anything for me! Thank goodness for Hail Bopp!

[Monque]

Lots of pretty green stars in that picture, I assume it's not true colour.
Any info regarding the filters used to produce this pic?

[sillyworm 2]

Thanks Ann for the Glen Yeuman link...I had lots of fun at that site.

[SK1]

C/2019 Y4 (ATLAS) may not be a single object but a group of objects. the next objects follow the first. This may explain the brightness change. We are observing the brightness of the group.

[Chris Peterson]

C/2019 Y4 (ATLAS) may not be a single object but a group of objects. the next objects follow the first. This may explain the brightness change. We are observing the brightness of the group.

All active comets brighten as they approach the Sun. This one is doing so a little faster than most, but its activity is far from unusual. Why would its brightness curve be better explained by multiple objects than by a single nucleus boiling off a lot of volatiles?