Tag: spiral galaxies

Andromeda's majestic spray of billions of hot stars

By Phil Plait | May 18, 2012 11:33 am

Well, what can I say about this devastating and jaw-dropping picture of our nearest spiral neighbor, the Andromeda Galaxy?

[Click to massive chainedmaidenate. Do it!]

Well, I could start with HOLY HALEAKALA!

This image is a collection of 11 separate observations of Andromeda taken by NASA’s GALEX satellite. Launched in 2003, GALEX (which stands for Galaxy Evolution Explorer) scans the sky in ultraviolet light, specifically targeting galaxies. Hot stars produce UV light, and so does the gas it illuminates, so by looking in the ultraviolet astronomers can learn about how galaxies are constructed. In the decade since its launch, GALEX has been phenomenally successful, cataloging hundreds of millions of galaxies, some as far as ten billion light years away!

This image of Andromeda is simply stunning. It’s comprised of two colors: what you see here as blue is higher-energy ultraviolet light, and red is lower energy (closer to the kind of light we see). Right away you can see that objects emitting the higher-energy UV are confined to the spiral arms, and lower-energy emitters are spread out across the galaxy. That’s exactly what I would expect: massive stars, the kind that really blast out UV, don’t live very long. They’re born, live out their short lives, and die (as supernovae) pretty much near the spot where they formed, which is in spiral arms. Lower mass stars live long enough to gradually move away from their nurseries, populating the rest of the galaxy.

Also, star formation at the very center of the galaxy probably occurred long ago and shut down, so we don’t see many or any massive stars there.

One thing I didn’t know is that the arms of Andromeda are more like rings! The galaxy is at such a narrow angle that it’s hard to tell, but if you trace the blue emission, the pattern does look more like a ring than a spiral. This jibes with earlier images in infrared taken by Spitzer Space Telescope (which I’ve inset here) and a huge and incredibly beautiful newer one taken with ESA’s Herschel far-infrared telescope (and OMFSM you want to click that link).

From what I’ve read, it’s not clear why the spiral arms appear to be more ring-like. Which I love. Why? Because Andromeda is the nearest big spiral galaxy in the sky, a mere 2.5 or so million light years away. It’s easily visible to the naked eye from a dark site, and I’ve seen it myself countless times using my own eyes, binoculars, and telescopes ranging from small ones up to Hubble. Yet there it is, in all its huge and obvious splendor and beauty, still able to surprise me. That rocks.

And a note about GALEX: NASA recently handed off its operations to Caltech, a very unusual move. The satellite was put into standby mode in February, and I was worried it would be shut down permanently. However, Caltech signed a three-year agreement with NASA — while NASA still owns the satellite, Caltech will now be in control of GALEX’s science mission, managing and operating it. At the end of the agreement it can be renegotiated if GALEX is still in good operating condition. This is an interesting idea, and I’m not sure how I feel about it. I love that GALEX gets to continue operations, but handing off science missions to private groups makes me a little uneasy. In this particular case I think it’s fine — Caltech is a research institute after all — but the precedent may have unforeseen consequences. We’ll see.

Still and all, it’s good to see new life breathed into an important and wonderful instrument like GALEX. I certainly hope it will continue to produce cutting-edge science for years to come… as well as amazingly beautiful images like this one.

Image credit: NASA/JPL-Caltech

Related Posts:

The cold arms and hot, hot heart of the fuzzy maiden
The first spectacular views of the sky from WISE
A Swift view of Andromeda
Andromeda’s warm glow
Andromeda: born out of a massive collision?

The start of a long, long dance

By Phil Plait | May 11, 2012 6:30 am

A hundred million light years away, two gorgeous spiral galaxies are locked in an embrace that may end with them merging, a dance spread across a hundred thousand light years in space and a hundred million years of time.

[Click to galactinate, and yeah, just do it. The hi-res version is big and lush and lovely indeed.]

This image, taken by frequent BABlog contributor Adam Block, shows this cosmic waltz in lovely detail (another wonderful image is available via the ESO as well [UPDATE: … and from Gemini, with a diagram of the two and a nice explanation]). The two galaxies (NGC 5426 on the left, and NGC 5427 on the right) are just starting this eons-long encounter, but affects are already visible. You can see tendrils of material stretching from NGC 5426 to its companion, drawn out by the force of NGC 5427’s gravitational attraction.

Inside the galaxies, you can easily see the pink glow of gas clouds, disturbed by the interaction, starting to furiously churn out hot young stars. Actually, stars of all masses are born in these clouds, but it’s the rare massive stars that have the most impact. They blast out ultraviolet light which makes the gas glow, and will explode as supernovae, lighting things up even more.

In galactic collisions like this the outcome can be difficult to ascertain. Perhaps they’ll pass this one time and do so with sufficient velocity to make this a one-eon stand, continuing on into the night. Or, if their relative speeds aren’t enough, they’ll pull apart, only to be drawn inexorably together once again. Even then they may pass, but this time in an ever-decreasing arc, until finally they merge into one bigger galaxy. Although this plays out over far too long a timespan to watch in real time, we see so many colliding galaxies that it’s like having snapshots at all different stages of evolution (see Related Posts below for lots of collidey goodness).

The general steps here are known, but the specific outcome of this particular encounter is still to be seen.

And we’ll see something like it up close, if not for quite some time: the Andromeda Galaxy will one day collide with our Milky Way, and when that happens we’ll be able to see what a galactic collision looks like… from the inside. Buy your tickets now. The show begins in just a billion years or two.

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Related Posts:

Desktop Project Part 25: Chaos in a galactic nursery
Sometimes a cigar galaxy is just a cigar galaxy
Galaxy cluster collision makes a splash… a million light years long!
First light for ALMA
Gorgeous galaxies celebrate Hubble’s 21st birthday
The delicate aftermath of cosmic violence

CATEGORIZED UNDER: Astronomy, Pretty pictures

The lovely faces and dark hearts of two galaxies

By Phil Plait | April 16, 2012 9:24 am

Spiral galaxies are among the most beautiful objects in the Universe. Their grand, majestic nature is sweeping on a scale of hundreds of thousands of light years; their delicate arms are composed of a hundred billion stars blurred into a milky stream; and as for their cores… well, that’s a different story.

Let me present to you two surpassingly beautiful galaxies, each with a dark secret in its heart.

First is NGC 4698, as seen by Adam Block using the 0.8 meter Schulman Telescope at Mt. Lemmon in Arizona:

[Click to galactinate.]

NGC 4698 is relatively close, at a distance of 60 million light years. This image is lovely, with the faint outer arms clearly visible, the inner arms lined with clouds of dust like black pearls on a string. The core looks odd, though, which I noticed right away. It’s brighter than I would’ve expected, and appearing almost as if it’s popping right out of the plane of the galaxy.

And here’s a second spiral, M77, one with which I’m fairly familiar — I spent a long evening photographing it for an observational astronomy class in grad school. This remarkable image, however, was constructed by Andre vd Hoeven, who downloaded dozens of Hubble images of M77 from the online archive, and painstakingly assembled them into this amazing shot:

[Click to embiggen.]

Wee see M77 a bit more face-on than NGC 4698, and by coincidence it’s also roughly 60 million light years away. The red glow dotting the arms is indicative of star formation; those are vast gas clouds glowing from the heat of young, hot stars embedded in them. It too is thick with dust, and like NGC 4698 the core looks… odd. Too bright, too compact. In the high-res version you can also see a greenish glow off to the left of the core, like a searchlight shining in that direction.

So both of these galaxies look normal at a perfunctory glance, but clearly have something else going on, something not obvious that makes them special. A secret, if you will. Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

A taste of WISE galaxies

By Phil Plait | May 26, 2011 7:00 am

The Wide-field Infrared Survey Explorer was turned off a few months ago, but the science it did lives on. NASA just released a gallery of nine spiral galaxy images taken by WISE, and they’re lovely:

[Click to galactinate.]

Several of my favorite big, grand design spirals are there, like M51, M81, and M83. Note that since WISE only sees infrared light, these are false color images; the colors used are blue for 3.4 micron IR light, cyan for 4.6 microns, green for 12 microns, and red for 22 microns. The reddest light a human eye can see is very roughly 0.75 microns, to give you a comparison. In the images, star-forming regions are yellowish and/or pink, dust (in the form of long-chain organic molecules called polycyclic aromatic hydrocarbons) is green, and old stars are blue.

While looking over the images, I actually recognized the name of the one in the lower right: IC 342 (here’s a full-res WISE shot of it). This is part of a small group of galaxies near our Milky Way that is heavily obscured by dust in our galaxy. Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

The belch of a gassy galaxy

By Phil Plait | May 15, 2011 7:00 am

Spiral galaxies are inherently interesting. Something about their beauty is so enticing… but when you look at them more carefully, the science and physics behind them is terrifically compelling. And when you use different eyes — say, radio telescopes — then you see something different entirely:

This shows two views of the lovely face-on spiral galaxy NGC 6946. On the left is a visible light image, and on the right is the radio view, taken by the Westerbork Synthesis Radio Telescope (taken over the course of 192 hours). Amazingly, these two images are to the same scale!

Spiral galaxies emit light across the entire electromagnetic spectrum, including visible and radio light, but what emits that light is different. Stars and warm gas emit visible light, but cold hydrogen glows at radio wavelengths. At a wavelength of 21 centimeters (about 8.5 inches, much, much longer wavelength than visible light, by a factor of tens of millions!) cold hydrogen can actually be quite bright, making it a perfect target for big radio telescopes.

In this image on the right I superposed both shots so you can see just how much more there is to NGC 6946 than the eye sees. What this image immediately tells us is that cold hydrogen extends well beyond the region where hydrogen is warmer, toward the center of the galaxy. It also shows the gas still takes on a spiral shape well past the visible boundaries of the galaxy.

A more detailed analysis indicates there are over 100 holes in the cold hydrogen gas as well, and these correspond to areas where stars are actively forming. That’s hardly a surprise! Stars use up hydrogen gas when forming, and then heat up what remains around them in the neighborhood. Once warmed up, the gas doesn’t emit as much 21cm radio waves.

The astronomers also found a lot of this gas is moving at high speeds, up to 100 km/sec (60 miles/second, fast enough to go from the Earth to the Moon in a little over an hour!). This is probably gas that’s been blown up and out of the galaxy by stars and supernovae, only to fall back down due to the gravity of the galaxy. That’s not known for sure, but we do see such fountains in other galaxies, including our own.

I’ll be honest: I’m more of a medium-to-high energy guy than radio guy. That’s why I tend to talk more about X-rays and gamma rays from astronomical objects, but every part of the spectrum tells a story. Radio astronomy has been around for almost a century now, and it is still and always will provide insight into the mechanisms behind the Universe.

Image credit: Rense Boomsma/Digitized Sky Survey/WSRT; ASTRON/JIVE Archive

Related posts:

When beauty and science collide
IR M63. What RU?
Two nearby galaxies peek out through the dust

CATEGORIZED UNDER: Astronomy, Pretty pictures

When beauty and science collide

By Phil Plait | March 31, 2011 7:00 am

I’ve been posting a lot of nice astronomical images lately, but sometimes one comes along and blows me completely away. How fantastically gorgeous is this?

Holy Haleakala! [Click to galactinate.]

That spiral galaxy is NGC 6872, and as you can see in this image from the Gemini South telescope it’s getting its clock cleaned by the littler spiral — IC 4970 — just to the right. The two are undergoing a galactic collision, a colossal event playing out over hundreds of millions of years. NGC 6872 is currently the victim here; its spiral arms are clearly distorted and being flung wide by the gravitational interaction. However, the smaller IC 4970 will be the ultimate loser in this battle: it will fall into the bigger galaxy, be torn apart, and eventually consumed in its entirety, becoming a part of NGC 6872. Bigger galaxies do this to smaller ones all the time; the Milky Way is in the process of eating several small galaxies even as you read this (I have details in articles linked below; see Related Posts).

This pair has been observed by other telescopes, including the composite picture here of images by the Spitzer Space Telescope (which sees in the infrared), The Very Large Telescope (visible light), and Chandra (X-rays), which I rotated to match the Gemini shot and rescaled a bit.
Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

IR M63. What RU?

By Phil Plait | March 4, 2011 7:00 am

Y’know, I’ve posted a lot of really pretty and cool pictures of spiral galaxies lately, and I’ve given descriptions of how they have black holes in their cores, and how the spiral arms form, and where stars are being born, and and and.

So you know what?

Boom! There you go. [Click to galactinate it.] No fancy explanations, no expounding on the ethereal beauty of dust lanes in an infrared picture from Spitzer, no lectures on anything. Just a really, really pretty picture.

I mean, I could mention how this galaxy, M63, is nearby at only 37 million light years, and how I’ve seen it myself through my telescope. But no, I won’t do that. Nothing about the prevalent short, stubby arms — called spurs — or ring of dust circling the core. And certainly nothing on how the starlight has been subtracted from the image so all you see is warm dust.

Nope. Just the picture.

Pretty, isn’t it?

Image credit: NASA/JPL-Caltech

Related posts:

Gallery: Spitzer’s greatest hits
The Milky Way’s (almost) identical twin
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CATEGORIZED UNDER: Astronomy, Pretty pictures

The Milky Way's (almost) identical twin

By Phil Plait | January 7, 2011 7:00 am

In my Top 14 Astronomy Pictures of 2010, I started off with a galaxy I called the Milky Way’s fraternal twin; it looks a lot like ours, but has some differences that were worth pointing out.

In one of those coincidences that makes me smile, only a few days later the folks at Hubble Space Telescope released another spiral galaxy image, and this one… well, it’s a beauty:


That’s really something! It’s so pretty I made it my desktop image. Click it to see it in all its 2800 x 2400 pixel galactaliciousness.

The name of this galaxy is UGC 12158. It’s a face-on barred spiral; the bar refers to that rectangular block of stars in the center. Some spirals have a spheroidal central bulge, like Andromeda does, but quite a few have a bar-shaped hub. The Milky Way does, in fact, and observations using radio and infrared telescopes (able to pierce the dust obscuring our view) show that our bar is actually pretty hefty. The small picture here shows an illustration of the Milky Way based on these observations, and we think it’s a pretty accurate representation. The resemblance to UGC 12158 is obvious.

When I first saw this Hubble picture, I was impressed with the beauty of this galaxy I had never seen before. But then I realized something… Y’know, I have a lot of experience looking at Hubble images. I spent years working on them, and after a while you get a feel for them. It’s just practice, and you get what almost feels like instinct about some things. So when I saw this picture and I got that odd (but familiar) feeling in my head, I knew to pursue it. It didn’t take me more than a few seconds to nail it down: this galaxy is big. The size of the star images, the smoothness of the galaxy itself, the way the image feels… I just knew that this was no tiny galaxy.

So I went to the release page for it, and when I saw the distance, I was shocked: that galaxy’s not big, it’s freaking huge. Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

A WISE view of a small neighbor

By Phil Plait | January 4, 2011 7:00 am

What shall be the first astronomical object to grace this blog in 2011*? With a whole sky to choose from, why not use an old friend, but seen in a surprisingly new way? So I present to you the nearby Triangulum Galaxy, M33, as seen by the orbiting far-infrared telescope WISE:

Yeah, that’ll do! Click to galactinate.

M33 is familiar to pretty much any serious amateur astronomer north of the Equator. It’s not that far in the sky from its bigger buddy M31, the Andromeda Galaxy, and in fact isn’t terribly far in space either; Andromeda is about 2.5 million light years away, while M33 is about 3 million. M33 is a spiral galaxy as well, and one of the closest to us.

Andromeda is probably the most well-known galaxy in the sky. So why is M33 so less famous? Mostly because it’s smaller; Andromeda and the Milky Way are roughly the same size (so close, in fact, that astronomers have been arguing for decades over which is the beefier of the two, and the title has swapped back and forth many times), but M33 is only half our size. Also, it’s more face-on to us, spreading its light out, making it actually a somewhat tough object to see. I’ve seen it in binoculars from dark sites, but it’s only marginally brighter than the sky background.

In the WISE image, blue and cyan are from infrared light at 3.4 and 4.6 microns (roughly 5 and 6.5 times the reddest light your eye can see). That comes mostly from stars. Green and red are IR at 12 and 22 microns, much farther in the infrared, and comes from cooler material like interstellar dust, which is opaque to visible light.

Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

Top Ten Astronomy Pictures of 2010 – Runners Up

By Phil Plait | December 20, 2010 6:30 am

When I made my Top 14 Astronomy Pictures of 2010, it was really tough cutting some out. This is a gallery of the images that, for whatever reasons, I decided to leave off. They’re still spectacular and gorgeous, though! Click on the thumbnail in the slider to go to an image, use the arrows to navigate back and forth, and click on the big image displayed below to get more info and a bigger version if available.


CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

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