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Cosmic Challenge: The Antennae


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Cosmic Challenge:

The Antennae

May 2017

Phil Harrington

This month's suggested aperture range:

Medium scopes

 

6- to 9.25-inch (15-23cm)

Target

Type

RA

DEC

Constellation

Magnitude

Size

The Antennae

Galaxy pair

12 01.9

-18 52.8

Corvus

~10.3

5'x2'

 

Although the four brightest stars in Corvus, the Crow, shine no more intensely than magnitude 2.6, the constellation's distinctive trapezoidal pattern in an otherwise star-poor region of the spring sky lets it stand out surprisingly well even in moderate light pollution.

We will put that to good use here as we probe for one of the best known pairs of interacting galaxies in the sky: NGC 4038 and NGC 4039, the "Antennae."

Above: Spring star map showing the location of this month's Cosmic Challenge.

Credit: Map adapted from Star Watch by Phil Harrington

 

Above: Finder chart for this month's Cosmic Challenge.  

Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window

Here, we find two galaxies in a celestial death match of tug o' war. Each is being yanked apart by the gravity of the other. As time goes on, the momentum built up lets each galaxy escape the other's grip, only to be inexorably drawn back together in the distant future to continue their head-to-head struggle. Although there is slim chance of individual stars colliding because of their wide spacing, each galaxy will eventually be distorted beyond recognition.

In the photo below, from the archives of the Hubble Space Telescope, we see clouds of bright pink and red ionized hydrogen surrounding blue star-forming regions intertwined with dark patches of dust. The rate of star formation is so high that the Antennae Galaxies are said to be "starburst galaxies." This won't last forever, however. Their struggle will continue, wrapping themselves around one an other, until eventually they have morphed into a single large elliptical galaxy.

Above: This image taken by the Hubble Space Telescope uses visible and near-infrared observations from HSTs Wide Field Camera 3 (WFC3), along with the Advanced Camera for Surveys (ACS).

Credit: ESA/Hubble & NASA

 

Keep in mind that as we gaze toward the Antennae, we are in a sense looking at the future of our Milky Way. In some 4 billion years, just as our Sun is about to run out of fusible hydrogen in its core, the Milky Way will collide with M31, the Andromeda Galaxy. Like the Antennae, the two will spar back and forth, eventually merging into a single system that many have already christened Milkomeda.

Trying to describe the unusual appearance of this intertwined pair has pushed the imaginations of observers to the limits. The most common nickname applied to the tight twosome is the Antennae, owing to the two long, contrail-like filaments extending from both in wider field photographs. These "antennae" are the result of tidal forces as the two galaxies graze one another. Others prefer the monikers Ring-Tail or Rat-Tail galaxies. Visually, the pair remind many of a comma, a shrimp, or even a tadpole when view through medium- and large-aperture backyard telescopes.

The table below lists individual specifics.

Target

Type

RA

DEC

Magnitude

Size

NGC 4038

Galaxy

12 01.9

-18 52.0

10.3

3.7'x1.7'

NGC 4039

Galaxy

12 01.9

-18 53.5

11.2

4.0'x2.2'

 

To zero in on the Antennae, we can use two of the stars in the Crow's body. Trace a line from the northeastern star, Algorab [Delta (δ) Corvi], to the northwestern star, Gienah [Gamma (γ) Corvi], and continue an equal distance to the southwest. As a reference, halfway along you'll pass a right triangle of 7th-magnitude stars. Continue in the same direction and you should find NGC 4038 and NGC 4039 set between two 9th-magnitude stars. This puts them just under a degree northeast of 5th-magnitude 31 Corvi.

At first glance, all you may see is a single 10th-magnitude glow. That's NGC 4038. What's so special about a description that could fit thousands of galaxies? Nothing until you take a closer look. At 100x or more, it should become clear that there is something different going on here. Look carefully and the amorphous glow will transform into a hook-shaped image with a faint extension coming off toward the south. This elongation is NGC 4039, and glows dimly at about 11th magnitude. A dark wedge intruding from the west separates the galaxies, as portrayed in my sketch here.

Above: The Antennae as sketched through the author's 8-inch (20cm) reflector.

Given rural skies that are free of horizon-hugging haze, neither galaxy appears uniform, but instead looks clumpy. That's not an illusion. You are seeing some of the consequences of the merging process, huge starburst areas where new suns are coming into being as we watch from afar. Knots along the rim of NGC 4038, the northern galaxy in the pair, are the most obvious, although some very subtle mottling is also evident in NGC 4039.

Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test. Contact me through my web site or post to this month's discussion forum.

Until next month, remember that half of the fun is the thrill of the chase. Game on!



About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy. Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2017 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.

 


  • CollinofAlabama, okiestarman56, John O'Hara and 2 others like this


15 Comments

Photo
M13 Observer
May 01 2017 01:52 PM

Seven decades ago, while scanning a Palomar Sky Survey plate of the area around brilliant Regulus in Leo the Lion, astronomers Robert Harrington (no relation) and A.G. Wilson noticed a faint blur of light just 1/2° north of the star. They may have thought at first that the glow was just an internal lens flare caused by stray starlight, but it soon became apparent that they had discovered something very real.

Click here to view the article

So, while the title refers to the Antennae in Corvus which the article linked to discusses, the blurb above refers to Leo I just above Regulus in the mane of Leo. Umm, what do the two have to do with each other?

So, while the title refers to the Antennae in Corvus which the article linked to discusses, the blurb above refers to Leo I just above Regulus in the mane of Leo. Umm, what do the two have to do with each other?

Only thing they share in common is that I wrote about Leo I last month and the Antennae this month.  Blurb corrected.

One of my favourite objects! Amazing in my 18"!

    • PhilH likes this
Photo
nicknacknock
May 02 2017 12:29 AM

Phil,

 

While the Antennae are for large apertures as you note, they are still visible from small apertures and were easy to identify with my 3" refractor from a dark site last Friday.

 

The level of image presented in the sketch is of course way beyond a mere 3", but one can tell even with 3" that it is not just one galaxy but two - due to the irregular shape appearing at the eyepiece.

 

As you very well put it, "remember that half of the fun is the thrill of the chase". Thanks for a great article!

    • PhilH likes this

I was testing out my C90 (old style) yesterday and decided to give it a shot. I had it in my FOV, I could see the two 8 and 9 mag stars right next to it, but I couldn't see the Antennae. I spent a good 40 minutes trying with a 25 mm and a 14mm ES 82°, but no bueno!

 

I was a little optimistic considering how easily I was able to see almost 10 mag stars in that small little scope. But the faint fuzzies are always tougher. Half moon didn't help, of course, and I was looking towards the city lights too. Gotta try again on a darker night.

 

Thanks!

    • PhilH likes this

I observed this pair last Saturday night at Lake Sonoma with my 22". But my favorite pair is the Siamese Twins in Virgo, NGC4567/68.

    • PhilH likes this

I observed this pair last Saturday night at Lake Sonoma with my 22". But my favorite pair is the Siamese Twins in Virgo, NGC4567/68.

Suggestion noted.  Thanks!

Photo
Luis Gabriel
May 03 2017 09:31 AM
    • PhilH and Nile like this
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faackanders2
May 03 2017 08:28 PM

I have looked in the past but never found them in my 17.5" f4.1 dob.  Now with Ethos I should give it a try again.

    • PhilH likes this
Photo
CollinofAlabama
May 17 2017 02:21 PM

Phil, you're definitely inspiring me to search it out.  Our Club has a couple of southerly dark sky astronomy sites where I might be able to catch this in my 8" dob.  I've never even tried for it, though I have seen it through friends' 12" and 20" scopes.  Always thought it was out of reach, but if you can find it from Long Island, New York in an 8" reflector, I certainly should be able to catch it from West Texas, and almost a kilometer above sea level.  Thanks for the challenge!  This will make a nice coupling with Omega Centauri this time of year.

    • PhilH likes this

Saw this successfully at a dark site. First through my 8" SCT. Then through a 18" Dob and finally through a 40" dob. The difference was pretty clear. The seeing wasn't perfect and couldn't see the flung out spiral arms. Thanks again for an interesting object.

    • PhilH likes this

I tried seeing this pair a few years back from my light-polluted condo.  I couldn't see anything in a 130mm refractor, 180mm mak or C9.25.  Was I looking in the wrong place?  Finally, I attached my DSLR to the 130mm and the Antennae magically appeared on a short time exposure exactly where I had been looking!!

    • PhilH likes this

I've observed this pair four times now and it's one of my favorites. Once each from Lake Hudson SP in Michigan, Deerlick Astronomy Village in Georgia, the Winter Star Party, and this past February at Chiefland Astronomy Village all using my 14.5" dob. My observation this past February was the best I've seen it. It's much easier down south than in Michigan, but it can be done. I was sitting on the ground and my alt bearing was very near the limit but I could see it just not real comfortably.  

    • PhilH and faackanders2 like this
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Chesterguy1
May 27 2017 05:17 PM

Saw this pair on 5/18/09 with my 15" according to my journal.  Am anxious to try with my 8" with a very good mirror, but also eight intervening years of progressive light pollution.  It's not terrible in that part of the sky, but may be enough to preclude viewing from my edge of small city location.  I'm finding fainter objects in the Herschel 400 in my backyard, viewing west, but that is definitely a darker part of the sky.  Tomorrow night is supposed to be more transparent with less cloud cover.  Wish me luck.

    • PhilH likes this
Photo
Chesterguy1
May 29 2017 08:42 AM

Well, I did manage to see it with my 8" last night, but I can't claim anything close to as impressive a view or sketch as the one generated by Mr. Harrington.  Sky conditions weren't bad with a tested SQM of 19.5.  However, my side yard is not protected from nuisance lighting and the woman across the street was having a party and had her garage lights on, which  kept entering my peripheral vision.  Additional magnification did not seem to clarify and the best I could discern was an irregular blob or patch at both 67x and 89x.  Perhaps 145x would have been better.  I could revisit it with the 15" as she doesn't keep the lights on all that often.  Corvus gets obscured by my neighbor's roof and trees by midnight so it has to be an early evening target and it won't be long before it's gone for the season.

 

I'm sure it would worth a jaunt west to a darker site (with unobstructed view of the southern sky) with either scope.  30 minutes will get me to a blue zone.

 

I also looked at two other H 400s in the same vicinity.  NGC 3962, a small elliptical galaxy in Crater that O'Meara lists as more difficult than 4038/39, but it's smaller and more condensed and I found it a bit easier, if quite small in my marginally light polluted neighborhood.  And the there's 4594, better known as M104, which looks good in almost any size scope.

 

Chesterguy



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