There is just something wonderful when Hubble points to nearby spiral galaxies. Sprawling and detailed, we get both great resolution on smaller features as well as a jaw-dropping overview of a grand spiral… like, say, NGC 1073:

Yeah, I know. [Click to galactinate -- I had to shrink it to fit here, and it lost a lot of the coolness when I did -- or grab the 3900 x 3000 pixel version.]

NGC 1073 is a decent-sized spiral galaxy about 60 million light years away. It’s actually part of a small, tight group of galaxies many of which are far more famous (like NGC 1068). But 1073 is important because of a simple property: it looks like us.

While it’s not a perfect match, NGC 1073 does bear an interesting resemblance to our Milky Way galaxy (UGC 12158 looks more like our galaxy, but is far bigger, for example). Both have large, rectangular bars going across their centers. Bars are a bit odd, since you’d expect the arms just to wind all the way down to the center. But the gravity of a galaxy isn’t like the gravity of a solar system, with a big heavy star sitting in the center. Galaxies have their mass spread out over a long distance, so what gas and dust clouds and stars feel in the way of gravity is different, and bars are a natural outcome of that. However, they’re still not perfectly understood. Bars may form when galaxies collide, and they might be an indication of a galaxy reaching middle age. Perhaps there are other factors as well.

Studying galaxies like NGC 1073 will help us understand how bars form, and why we have one too. Remember, we’re stuck inside our galaxy and can’t see it from the outside (that picture above is an illustration based on detailed observations). It really helps our understanding of the Milky Way to observe galaxies like ours.

An important thing too is that the two galaxies are different in some ways: NGC 1073 has more open arms, for example, compared to our more tightly wound arms. Those differences are telling us something as well. What is it that makes one galaxy hold its arms closer in, and another to fling them out? Why does this galaxy have two arms, and that one three? If you can look at two galaxies that are alike except in one way, it’s easier to isolate the cause. So studying NGC 1073 is a great way to study ourselves.

It always makes me think of Nietzsche, who wrote on the nature of man, "And when you gaze long into an abyss, the abyss also gazes into you."

But on the nature of the Universe, it changes: "And when you gaze long into an abyss, your gaze falls back on yourself."

Well, this is depressing: Fomalhaut b may not exist.

Fomalhaut is one of the brightest stars in the sky, and is only about 25 light years away — that’s close, on a cosmic scale. It’s young, not more than a few hundred million years old, and surrounded by a vast ring of dust, leftover from the formation of the star itself. The ring is about 20 billion km (12 billion miles) in radius, and has a sharp inner edge.

That last bit is important: the easiest way we know to make the inside edge that well-defined is if a planet is orbiting the star just inside the ring. Its gravity would draw in particles, sculpting what would otherwise be a fuzzy boundary into a clean-cut ring. Not only that, but the ring is off-center; again, that’s likely due to the gravitational influence of a planet.

In 2008, astronomers announced they had found that planet: it appeared in two different Hubble Space Telescope images (shown above; click to embiggen) separated by two years. During that time, it had moved a little bit, by just what you’d expect for a planet at that distance from the star. The news came out the same day as other planets were seen around a different star, and I, along with lots of other folks, made it a headline (see the gallery at the bottom of this post showing all the planets we’ve been able to detect directly in images). This was, after all the first direct detection of a planet orbiting a Sun-like star!

Except, maybe not so much. A new paper has come out (PDF) trying to see Fomalhaut b using the Spitzer Space Telescope. Spitzer is sensitive to infrared, where the planet is far brighter.

And what did they see? Nothing.

Dang.

This image is pretty damning for the existence of Fomalhaut b. It’s the Spitzer infrared observations of the star, with the star’s light carefully removed. On the left is the actual image, and on the right they artificially added a point of light calculated to be equal to what the planet would emit, in the same position the planet should be — that’s what Arrow 1 is pointing at. It should be one of the brightest things in the image (Arrow 2 points to an unrelated bright spot). And while it’s obvious on the right, nothing can be seen on the left, in the real image. In other words, the planet isn’t seen.

Dang again.

Looking over the paper, it’s clear the astronomers were very careful, and did a number of tests. There’s no known way to make a planet as bright as what was seen in the Hubble images yet invisible in the Spitzer images. If the planet were there, they should’ve seen it. Also, a recent study has shown that if the two images show the planet moving, it would be on an orbit that crosses the ring! That seems extremely unlikely, if not outright impossible. A planet that big and massive — more massive than Jupiter — would disrupt the ring in short order if it physically crossed it. That really does make it very, very likely this is not a planet^*.

So what is it? It’s probably a clump of dust orbiting the star, reflecting light from the star enough to show up in the Hubble images but not warm enough to show up in the infrared observations.

That’s too bad. If this is true — and it probably is — then that takes away one of the very few planets directly seen in telescopic observations. However, there are still plenty more, and those have been confirmed (again, see the gallery below). And that number will tend to increase as time goes on, even if every now and again it drops by one or two.

Hmph. I once wrote that destroying a planet is hard. Sometimes, all you need to do is try to observe it a different way, and poof! It’s gone.

And now I have to update that gallery, and all my previous pages about it too. Dang science. Always learning more stuff and changing what we thought we knew.

Image credit: Paul Kalas, U C Berkeley; NASA/Spitzer/Markus Janson et al.

^* I chatted with an astronomer friend of mine about this, and he agreed with the authors of this new study. "Overall," he wrote me, "it smells like fish.". I couldn’t help myself. I wrote him back: "Of course it does. Fomalhaut is the brightest star in Pisces!"

[Below is a gallery of exoplanets that have been directly imaged using telescopes on ground and in space. Click the thumbnail picture to get a bigger picture and more information, and scroll through the gallery using the left and right arrows.]

---

What would sunset look like if you were on the planet HD209458b, a gas giant orbiting a star 150 light years away? According to exoplanetary scientist Frédéric Pont, it looks like this:

Isn’t that pretty? And there’s quite a bit of science in that, too.

First things first: HD209458 is a star pretty similar to our Sun. It was one of the first stars determined to have a planet orbiting it (way back in 1999) — the aforementioned HD209458b, nicknamed Osiris — and it turns out the planet’s orbit is so close to edge-on as seen from Earth that we see that planet passing directly in between us and that star once per orbit. When the planet transits that star the amount of light we see dips a little bit. From that we can get the period of the orbit and the size of the planet (a bigger planet blocks more light).

But we can get more, too. There’s a camera on board Hubble called the Space Telescope Imaging Spectrograph, or STIS. It can take the light from an object and break it up into thousands of separate narrowly sliced colors, called a spectrum. By analyzing that spectrum we can find out an astonishing amount of things about astronomical objects: their temperature, rotation, even their composition!

Shortly after HD209458b was discovered to be a transiting exoplanet, STIS was pointed at the star. The camera took hundreds of very short exposures during a transit in the hope of being able to detect the atmosphere of the planet. Osiris was known to be massive, about 70% as massive as Jupiter, so it most likely has a thick atmosphere. It also orbits so close to its parent star — 6.7 million km (4 million miles), much closer than Mercury orbits the Sun — that the heat from the star puffs the atmosphere up, making it easier to see.

In fact, the spectra did reveal the presence of an atmosphere; the first time the atmosphere of an alien planet was ever observed. Different elements and molecules absorb light at different colors, so in the spectrum there are dark spots where the planet’s air absorbs the light from the star behind it during a transit, and how dark that spot gets tells you how much light is absorbed.

It’s this information Prof. Pont used to create the image above (inspired by investigation and an animation done by Alain Lecavelier des Etangs). By knowing the color of the star itself, and using the way the planet’s atmosphere absorbs light, he created this image of the star using sophisticated computer modeling. (more…)

Astronomical imagery is a tricky business. Different objects behave differently, emitting light in different ways. So, for example, a cool dinky star might give off very little blue light — through a blue filter it virtually disappears — while a hot, massive star blasts out blue light. Your choice of filter can drastically change the way an object looks.

Having said that, I recognized right away that this image is the core of the nearby galaxy M82… but it still looks funny to me:

[Click to galactinate, or grab the huge 12.5 Mb image.]

One reason this new image from Hubble looks funny to me is that there aren’t as many stars in it as I expect. M82, also called the Cigar Galaxy due to its elongated shape, is pretty close as galaxies go, about 12 million light years away. It’s one of the closest large galaxies in the Universe, and a Hubble image usually shows it littered with stars, so closely packed they form a bluish background glow in most pictures.

And while that background of stars is there, it’s more diminished than usual because in this image astronomers used a series of filters that accentuate the light emitted by gas. While stars put out this kind of light as well, these filters downplay starlight and crank up the volume on, um, gaslight. Specifically, blue and green are from oxygen, red is from sulfur, and teal is hydrogen. The dark material is dust: long-chain molecules that absorb starlight. They also tend to redden light coming from behind them, similar to the way haze in the air makes sunsets look red.

Clearly, M82 is lousy with gas and dust in its core. (more…)

160,000 light years away sits the Large Magellanic Cloud, an irregular dwarf galaxy that orbits our own Milky Way galaxy. It’s a fascinating object, actually, filled with stars, gas, dust, and all the usual trinkets a galaxy has.

It also has an assortment of globular clusters — roughly spherical collections of a few hundred thousand stars bound by their own gravity orbiting the cluster center like bees buzzing around a hive. NGC 1846 is one such globular cluster, and it looks like most of the others, if a bit sparse and loosely distributed. But it has something that does make it rather special. You can see it if you peruse this lovely Hubble Space Telescope picture that was just released:

[Click to embiggen, or get a much larger version.]

Isn’t that pretty? As much as I like it, the most interesting thing in it, though is actually rather difficult to see here. Look at the center of the cluster, then let your eye go straight down, nearly to the bottom of the frame. See the green spark there? It’s the only green thing in the entire picture. It’s not a star — there are no green stars — but it used to be…
(more…)

Before I do anything else, I simply have to present this insanely cool Hubble image of the galaxy cluster MACS J1206, which lies at the mind-numbing distance of 4.5 billion light years from Earth:

[Click to enclusternate, or grab the bigger 2564 x 2328 pixel version.]

Like I said, insanely cool. The cluster has thousands of galaxies in it, and a total mass of something like a quadrillion — that’s 1,000,000,000,000,000 — times the mass of our Sun!

The image was taken as part of a program called CLASH, for Cluster Lensing And Supernova survey with Hubble. A large group of astronomers from ten different countries are observing more than two dozen such distant clusters to look for many interesting things, including exploding stars (which help us gauge the expansion rate of the Universe), very distant galaxies (to help us understand the early Universe), and to look for dark matter.

Dark matter is stuff that doesn’t emit light, but has mass. Careful observations over the years have ruled out pretty much every form of normal matter we can think of, from simple hydrogen clouds to black holes. Whatever this stuff is, it’s weird, not matter as we know it.

But we do know it’s there. Its gravity affects how spiral galaxies rotate, how clusters like MACS 1206 stay together, and can even bend light from more distant galaxies as it passes through. That last bit is the big deal here.

(more…)