Bad Astronomy
The entire universe in blog form

July 29 2015 7:15 AM

The Densest Galaxies Ever Discovered

I think one of the most interesting facts in astronomy is a simple one to state: Galaxies are cannibals. They eat each other.

The Milky Way grew huge this way; our galaxy is in the top tier of spirals in the Universe. (Many are bigger, but the vast majority are far smaller.) It got that way by colliding and merging with smaller galaxies, enlarging its ranks over time. It’s actually in the process of eating several dwarf galaxies right now. Like, literally, at this very moment.


But what of these smaller galaxies? What happens to them?

Some merge completely with the bigger galaxy, a completely digestible meal. But sometimes parts of the smaller galaxy survive. If the center is compact and dense enough, it can make it through the ordeal.

We’ve seen these here and there, but now astronomers have found a new class of such objects: Ultra Compact Dwarfs, or UCDs. And it turns out they’ve been hiding in plain sight.

These galaxies are small and luminous, and incredibly dense with stars. Through ground-based telescopes they’re so small they look like foreground stars, and through Hubble their dense nature but slightly visible fuzzy halos that make them look like distant galaxies. That’s how they avoided discovery for so long: They slipped between the cracks.

These objects are the densest galaxies known. Our Milky Way has hundreds of billions of stars, but they’re spread out over a hundred thousand light-years. One of the new UCDs just discovered has far fewer stars—something like 10 million—but it’s only about 20 light-years across!

NGC 6934
NGC 6934, a typical globular cluster. A UCD would be about the same size, but have 10-to-100 times as many stars in it.

Phto by ESA/Hubble & NASA

That’s really weird. I mean, really weird. It has the size of a typical globular cluster (a spherical cluster containing a hundred thousand stars or so) but is a hundred times denser!

Another UCD found is less extreme but still pretty amazing: It’s about 200 light-years across and has a hundred million stars in it. That’s far larger than a globular cluster, with a lot more stars.

It’s their incredibly compact nature that helped them survive being a galactic snack. This video should help make that clear:

The small galaxy is in a tight orbit around the center of a much larger galaxy. Tides from the big galaxy strip the outer stars off the smaller one; in a sense the gravity they feel from the bigger galaxy is larger, so they get peeled away from the smaller one. Stars closer in to the center of the small galaxy are more tightly bound, and stay together.

After a few passes all the outer stars are ripped away, and what’s left is just the compact nucleus of the smaller galaxy: an ultra compact dwarf. In fact, spectra taken of the UCDs show they resemble the cores of galaxies.

You’d expect to find these objects near bigger galaxies, and sure enough both of the new objects are physically close to much beefier galaxies. Note only that the larger galaxies show signs of recent disturbances (basically, weird overall shapes) indicating they recently underwent a collision and merger.

This work is impressive. It’s not often you find a new kind of astronomical object, especially when examples of them are sitting right in images that have been around for years. But their borderline nature between star clusters and proper galaxies effectively hid them.

I’ve long said that we have to be careful and not let our prejudices blind us to objects that are neither one thing or another (cough cough Pluto cough). In this case, I’m glad this team was able to see these UCDs for what they are.

And I have to add: The astronomers who found them were undergrads, students at San José State University! They combed through archived data taken by several different telescopes to identify potential ultra compact galaxies, then followed up using observations to nail down their characteristics. It’s quite an accomplishment!

And a reminder to not always dismiss something just because it conforms to your own predisposed beliefs. Look around you! What are you missing? 

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July 28 2015 1:16 PM

Sen: Is Kepler-452b Really Earthlike?

I recently wrote about the newly discovered exoplanet Kepler-452b. It’s bigger than Earth, but it orbits its Sunlike star in the habitable zone, where water could ostensibly exist on the planet’s surface.

The planet is actually 1.6 times the Earth’s diameter, and if I were a betting man, I’d wager it’s not Earthlike at all. Given what we think we understand about planets, it’s as likely to have a thick atmosphere like Neptune's as one like Earth's. Maybe more likely. But we just don’t know.


Despite this, a lot of headlines were screaming about an Earthlike planet found, calling it “Earth’s twin.” Feh.

In fact, I feel “feh” so strongly that I wrote all about this for my biweekly column for You can go there to get the details of my “feh”-ness. It’s subscription only, but that includes getting lots of articles by lots of good writers … and there are more to come. You’ll like it.

And to be clear: I am excited about the discovery of this planet, and its implications. I just wish stuff like this weren't overhyped.

July 28 2015 7:15 AM

Because Comets Aren’t Cool Enough: They Also Have Sinkholes

“No, no. We have already succeeded. I mean, what are the terrors of the Comet? One, the ice venting—no problem. There's a popping sound preceding each; we can avoid that. Two, the sinkhole, which you were clever enough to discover what that looks like, so in the future we can avoid that too.”

—The Dread Astronomer Westley Roberts


The comet 67P/Churyumov-Gerasimenko is heading toward the Sun, and as it does, it slowly dies.

But what a death. Underneath its crusty surface are icy deposits, and as the comet nears the Sun, these warm. The ice turns directly to gas and blows out of vents, forming gorgeous and delicate streamers of water vapor dozens of kilometers long. The picture at the top of the article shows the long-distance view of this; from 177 kilometers away, the Rosetta spacecraft sees quite a few of these jets.

But what do these do to the surface? Some of the vents have been seen in close-up views from Rosetta, and they come from pits that you might mistake for impact craters at first. It’s clear these are the sources of at least some of the jets, but a new study reveals they’re more than that: They’re sinkholes.

A 200 meter wide sinkhole on a comet (and it's so cool just to type that). The walls are steep, and you can see jets of vapor moving across it. The overexposed parts are the comet's surface.

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; graphic from J-B Vincent et al (2015)

Sinkholes on Earth are relatively common; water (for example) can erode away material under the surface, and at some point gravity takes over, and the structural integrity gives way. The surface collapses, sometimes taking cars or even houses with it.

On a comet things are slightly different. For one, the gravity is only a tiny fraction of Earth’s. For another, sinkholes on Earth tend not to jet towers of water vapor out from them.

But the overall idea is the same. Heat from the Sun warms the comet. This heat leaks under the surface (possibly through cracks) and turns the ice into gas, which then leaks out. Eventually a large cavity is formed under the surface, so big that the “roof” of material over it collapses, forming the steep-walled sinkholes.

This allows light to flood in, which can heat the ice rapidly, causing an outburst of jetting from the comet. This has been seen on 67P, too. Eventually, the walls of the hole erode as more ice vaporizes, and the steep pits become more shallow. Quite a few of these are seen on 67P as well. This means the steep pits are young, and the shallow ones old.

While this result doesn’t surprise me—it’s been suspected since the first close-up pictures came back from Rosetta—it’s nice to see the whole story figured out, and an explanation found for the steep pits.

Comets are so cool. And this one has turned out to be a fantastic choice for an extended visit by Rosetta. We’re learning so much about these interplanetary wanderers, and, unsurprisingly, it’s all been really amazing.

July 27 2015 7:00 AM

Gardasil: Yup, Still Safe

Through an article in Forbes I saw that a new study has been published about the safety of Gardasil, a vaccine for prevention of certain strains of human papillomavirus, or HPV.

HPV is a virus that can lead to genital warts, many types of cancer, and cervical cancer in women, which kills 4,000 women every year in the U.S. alone.


The Gardasil vaccine, on the other hand, caused some people to faint after getting it, and others got mild skin infections—both of which occur somewhat rarely with other vaccines too, as you might expect.

Which sounds worse to you?

The study, published in the Pediatric Infectious Disease Journal, looked at the published data about effects from the vaccine and found that it has a “favorable safety profile.” This study comes after many other previous studies that show essentially the same thing. There is no correlation between getting the Gardasil vaccine and seriously adverse effects such as “autoimmune diseases (including Guillain-Barre Syndrome and multiple sclerosis), anaphylaxis, venous thromboembolism, and stroke.”

Mind you, all these things and more have been used by people who attack vaccines as an argument against it. And, just like essentially every claim made by the anti-vaccination movement, these arguments are wrong.

That doesn’t stop them from making them, or from them getting attention by mainstream media; attention they most assuredly do not deserve.

It’s very frustrating; mounds of data show these vaccinations are incredibly low-risk, but it only takes a little bit of doubt and fear to make vaccine rates drop. For example, a young girl died tragically not long after getting the vaccine, and it got a lot of press, but it was later found that she died of a completely unrelated cause. This, sadly, is expected; more than 178 million doses of Gardasil have been given worldwide, and given that huge number it’s a statistical certainty that some young people will die not long after getting them. But as the saying goes, correlation is not causation. The vaccines are not to blame here.

Even more frustrating about this vaccine is that it’s being fought by an unusual group of people; while most anti-vax leanings are not affiliated with any particular political persuasion, Gardasil gets attacked additionally by conservatives who think that girls getting it will become more promiscuous, because HPV is a sexually transmitted disease.

However, this has been shown to be false. Worse, these same people tend to promote abstinence-only education, which has been shown conclusively to be the worst possible sex education; kids taught his way tend to have more pregnancies and more STIs than ones who are taught progressive, healthy sex ed.

It’s like Bizarro world, where everything is backward. All the evidence shows Gardasil to be safe and to be effective against a virus that causes horrific illnesses. It also shows that the claims made by anti-vaxxers are wrong, and that people fighting the vaccine because of their own sexual biases are making things far worse.

And yet they dig in. They insist real science is wrong, that their anecdotes are better, that the entire medical industry is on the take (which is silly beyond reason).

But that’s where we are. When it comes to health issues, especially ones tied to sexuality, reason goes out the window and emotions take over.

That’s why I am very, very clear about this: I and my family are all up to date with our vaccinations, and my daughter has had all three stages of the Gardasil vaccine (we’d have done that if she had been a boy, too). As a parent, as someone who knows and loves someone with an autoimmune disorder, and as a person who knows just how truly awful so many diseases are and how easily and safely they can be prevented, I am a strong advocate for vaccinations.

It’s your body, but it affects literally everyone around you. Don’t listen to the anti-vaxxers, who just want to scare you. Get the facts. And please, talk to your board-certified doctor and find out if there are any vaccinations you need.

How many lives will you save when you do?

Tip o’ the virion to the Refutations of Anti-Vaccine Memes group on Facebook.

July 26 2015 7:00 AM

Journey From the Far Side of the Sun

Studying the Sun from Earth can be frustrating. From 150 million kilometers away, we can only see one side at a time. Sure, the Sun rotates, so we see the whole thing over the course of about a month, but sometimes you want to see it from different angles at the same time, like when it shoots out an explosive flare or coronal mass ejection.

What you want is a stereo view. Or STEREO.


STEREO is the Solar TErrestrial RElations Observatory, a pair of Sun-orbiting satellites; one is in a slightly smaller orbit than Earth so it travels ahead of our planet and the other in a slightly larger one so it lags behind. Over time, they get far enough apart to see the Sun from totally different viewpoints.

Right now, STEREO-A (A for Ahead) is almost directly opposite the Sun from us. In fact, it was behind the Sun for a few days, but even before and after that it was so close to our star that communicating with it was not possible.

The image above, taken in the far ultraviolet, was one of the first to come back from STEREO-A, on July 15 (around the same time New Horizons was sailing past Pluto 15 times farther away from us). At this wavelength, magnetic activity glows fiercely, and you can easily see the towering loops of the Sun’s complex magnetic field piercing the surface and arcing a hundred thousand kilometers above the surface.

This is the same magnetic activity, incidentally, that will not cause an ice age on Earth. Not that it isn’t dangerous.

STEREO has provided a huge amount of benefit to solar astronomers trying to figure out the ridiculously complicated behavior of our nearest tame nuclear inferno.

Sometimes, though, what it does is just plain cool … like the time it saw the Moon pass in front of the Sun. It’s a solar eclipse like you’ve never seen before.

We learn a vast amount of important, crucial, information from space-based astronomical observatories. But also, they just increase the coolness of our lives.

My apologies to Gerry Anderson for the title of this post.

July 25 2015 7:00 AM

Hey! It’s Not Rocket Science!

I mentioned in a recent post that I met astronaut Chris Hadfield at Comic-Con in early July. Chris is the real deal: He is a friendly, funny, warm, intelligent, and hard-working human being who truly and passionately wants to make the world a better place.

One way to do that is to get more people interested in science. To do that, he’s helping create (and starring in!) an animated comedy science series called “It’s Not Rocket Science,” which will premier this fall.


The series is being made with the help of his son, Evan. It was Evan’s idea for his dad to make the “Space Oddity” video, in case you’re wondering if Evan is up to the task (he edited it all together, too). Evan has also been helpful to me a few times pinning down some of the photos from space Chris took when he was on the International Space Station, too.

As for the animation, rest assured that’ll be great too. How do I know? Because my friends Tracy King And DC Turner are doing that! They made Tim Minchin’s brilliant song “Storm” into an equally brilliant animated video.

The animated series will be free on YouTube, but they’re supporting it via Patreon. If you pledge to it, you can get lots of bonuses, like graphics, wallpapers, mention in the credits, and even signed swag from Chris.

They’re making 10 videos, and I am seriously really excited to see them! This is a fantastic team of people, and I know the series will be great.

So throw some filthy lucre their way, and keep your brain ready for this. You’ll be glad you did. In the meantime follow Chris, Evan, Tracy, and DC on Twitter, to keep up with the news on the show.

And because why not, here's "Storm." It's amazing.

July 24 2015 3:00 PM

New Horizons Looks Over Its Shoulder at Pluto

I’ve been expecting—and seeing—amazing images of Pluto from the close approach flyby of the New Horizons probe from mid-July. And even though I knew the images taken once the spacecraft was past Pluto would be lovely, I still wasn’t quite prepared for just how awe-inspiring they would be.


July 24 2015 12:47 PM

Full-On Pluto

While I’m waiting for a press conference on Pluto in a couple of hours (18:00 UTC), I thought I’d show you this beautiful image of Pluto’s face released by NASA this morning. It’s a composite of high-resolution data from the black-and-white (well, grayscale) LORRI camera combined with color data from the Ralph camera.

The colors have been enhanced to bring out overall patterns and regional differences. The images were taken on July 14, when New Horizons was 450,000 kilometers from Pluto—not much farther than the Moon is from Earth!


Several things strike me right away. We see lots of craters, many of which look eroded from time. It looks like there are faults or canyons running here and there across the surface. Also, some of the colors appear as “streaks,” making them look wind-blown or the result of some kind of fluid flow.

Having said that, I am totally guessing here. We must have a care not to overinterpret low-res data like this! Also, I’m no expert, but I hope that the experts today will comment on some of these features. No doubt more detailed images will be released soon, so stay tuned!

July 24 2015 7:00 AM

Crash Course Astronomy: Stars

You’re the only star in heaven,
You’re the only star that shines,
You’re the only star in heaven,
Now that only star is mine.
            Frankie Goes to Hollywood, “The Only Star in Heaven”

Stars are the building blocks of the visible Universe. They’re the fundamental unit, like atoms in matter. Stars make up galaxies, and galaxies make up the Universe.

They are also why we’re here, quite literally. Stars make planets, and stars make the elements that make you and me. We owe our existence to stars.

So understanding them is kinda critical to understanding, well, everything. Wanna know more? Then do I have a Crash Course Astronomy episode for you!

Mea culpa: In the “Focus On” segment, I say that the Sun’s spectrum peaks in the green. To be fair, it peaks in the blue-green part, and atmospheric absorption makes the light that hits the ground peak more in the blue. But when you add it all up, the Sun emits more green than blue light, which is what I meant. I should’ve been more clear.

I wrote about why there are no green stars in a post a few years back. Not that there aren’t green objects in space. But those are different. Comets can look green too.

And don’t confuse any of this with Hank Green in space. That’s a completely different topic.

July 23 2015 1:13 PM

Astronomers Find a Near-Earth-Size Planet in the Habitable Zone of a Very Sunlike Star

One of the biggest goals in the search for exoplanets—alien worlds—is finding an Earth-size planet orbiting its star in the “habitable zone,” where liquid water might exist on its surface. In other words, finding another Earth.

So far, a dozen such planets have been found. All of those planets may be very much like Earth (we can’t be sure, as I’ll get to in a sec), but they orbit smaller, cooler stars than our Sun.


On Thursday, astronomers announced they have found another planet in its star's habitable zone: Kepler-452b. But this one is different: It orbits a star much more like the Sun. The star and planet are about 1,400 light-years away.

The planet was discovered using what’s called the transit method; as it orbits its star, we see that orbit edge-on. Once every orbit, the planet passes directly in front of the star and we see a tiny dip in sunlight. The size of that dip tells us the size of the planet, and the time it takes tells us the planet’s orbital period.

Kepler-452b orbits its star at a distance just 5 percent more than Earth orbits the Sun, with a year 385 days long. While the star is similar to the Sun, it’s older, and stars brighten as they age. That means Kepler-452b actually receives more heat from the star than we do from the Sun, so it’s likely warmer than we are.

Note, though, that a couple of billion years ago the star was cooler, pretty much like the Sun is now. That means that a long time ago, 452b was getting the same amount of light and heat we do. Interesting.

This doesn’t mean the planet is Earthlike, though. For one thing, it’s bigger than we are: Its diameter is 1.6 times that of Earth. We don’t know its mass, unfortunately, and without that we can’t know its density. The density is what gives us our first clue about what the planet’s made of; water has a density of 1 gram per cc, but iron is 8. Rock is 2–3.

If the planet has the same stuff in it as Earth does, it’ll be more massive; four times Earth’s mass*. In that case, its surface gravity would be 1.6 times Earth. If you weighed 100 pounds on Earth, you’d weight 160 pounds there. But only if it’s rock and metal like we are. If it’s less dense (more rock) than, the surface gravity will be lower; if it’s denser (more metallic), it’ll be even higher.

It’s not clear what that means for a planet’s atmosphere. All other things being equal, more gravity means it can hold on to more gas, so the air there could be much thicker. If so—and remembering it’s receiving more light and heat from its star than we do—it might be suffering a runaway greenhouse effect. Or, it may not have any air at all. Or or or. Without more information, we can only guess.

452b and 186f
Comparing Kepler-186f and -452b. The orbit of 186f is smaller, but the star is much cooler, so the planet will have roughly the same amount of light and heat from its star as Earth does from the Sun.

Drawing by NASA/JPL-CalTech/R. Hurt

This is an exciting discovery, since this is the first exoplanet roughly Earth-size in the habitable zone of a star so much like our own. The last time we found one this good was Kepler-186f, which orbits a red dwarf. That planet is much closer to our size than 452b is, and may be more similar to us. It’s not clear there how orbiting a red dwarf would make it different. Would the atmosphere be different? If life existed there, how might it look?

I’m a little torn about this discovery. For decades we had no idea if other planets even existed around other stars. Now we know of thousands! And we also know of many that are the size of our Earth, meaning they aren’t too hard to make. In fact, we think there are billions of Earth-size planets in our galaxy alone! Most will be too hot or cold for life, or have other issues making them likely to be uninhabitable.

Searching for a planet with conditions as close to ours is a clear goal here. Kepler-452b is a big step in that direction.

Exoplanets in the habitable zones of their stars. Open circles are candidates (not yet confirmed). Filled blue dots are from older catalogs; yellow ones are from a new release of observations from Kepler. Bigger stars are higher up in the graph, and the amount of light/heat the planet receives is on the horizontal axis (1.0 is equal to what we enjoy here on Earth, with cooler planets to the right).

Drawing by NASA/N. Batalha and W. Stenzel

But it’s not perfect. It’s bigger, the star is hotter, and so on. I suspect 186f might be more Earthlike, but again we can’t know for sure. So I don’t want to overhype this discovery.

We need bigger telescopes, ones capable of teasing out the planet’s light from the star’s, taking its spectrum, and analyzing that spectrum for tell-take signs of chemistry. From that we can gauge its temperature better, what it’s made of, and even if there are biological markers (like, say the presence of oxygen molecules, which are hard to keep around without biology). Until then, we just don’t know enough about these planets to say much more about them with certainty.

And I think what may be even more important is to see just how diverse Earth-size planets are! Some bigger, some smaller, some hotter, some cooler. The interesting point here is that nature is cooking planets with all sorts of different flavors here, and while looking into the heavens and seeking out one that looks like us is natural, we should also be careful to delight in the varying recipes out there.

The big question we ask is, Are we alone? The answer, I suspect, hangs on what you mean by “alone.” We are in a galaxy brimming with planets, many of which look like us, and many of which don’t. But even the ones that look different at first may be more like us than we know.

* The volume of a sphere increases with the cube of the radius. Since Kepler-452b is 1.6 times the radius of Earth, its volume is 1.6 x 1.6 x 1.6 = 4.1 times Earth's volume.