Bad Astronomy
The entire universe in blog form

June 29 2015 7:00 AM

Weighing a Galactic Monster 

How do you weigh a black hole?

That is, to be more precise (or pedantic), how do you figure out what the mass of a black hole is?


There are actually lots of ways, but they all depend on a very simple law of gravity: If you’re orbiting something (whether it’s a black hole, a star, a planet, or anything else), the closer you are, the faster you’ll go.

If you start there, and make a few assumptions, then all you need to do is observe stuff orbiting the black hole, figure out how quickly it’s moving, and boom. The black hole mass falls out.

Astronomers have been doing this for a long time. Observing stars in motion—literally, watching them physically move over several years—in the center of our own Milky Way galaxy shows that the supermassive black hole residing there has a mass of more than 4 million times that of our Sun.

Another way is to look at the motion of stars and gas in another galaxy. We can’t see their stars moving directly, but as they zip around the central black hole, sometimes they move toward us and sometimes away. That creates a Doppler shift, a shifting of the light emitted toward the blue and red end of the spectrum. The amount of Doppler shift depends on the velocity of the population of stars and/or gas as they orbit, and that means you can get the black hole mass that way. For example, gas in the center of the galaxy M84 was used to find its black hole has a mass of over a billion times that of the Sun!

Now astronomers have used a different way, though based on this same idea. They used ALMA, the Atacama Large Millimeter/submillimeter Array, to look at light emitted by the molecules HCN (hydrogen cyanide) and HCO (there’s no specific formal name I could find for this, but it’s a carbon atom bonded to an oxygen and hydrogen atom) in the galaxy NGC 1097. ALMA is very precise, and they were able to find both the location of the gas and its velocity.

Coiled Creature of the Night
NGC 1097 as seen by the Spitzer Space Telescope in infrared, showing the entire galaxy. The tiny ring at the center is the ring seen in the top photo.

Photo by NASA/JPL-Caltech/The SINGS Team (SSC/Caltech)

This gas orbits well outside the black hole, and there are stars there too, millions of them. To account for them (because if they don’t, they’ll get too high a mass for the black hole) they used Hubble observations of NGC 1097. They then fit a series of models, each using different black hole masses, to see which one fit the observed velocity of gas best.

Their result: NGC 1097 has a 140 million solar mass central black hole. That’s way beefier than ours. Also a bit higher than previous estimates of 100–120 million.

The reason this is important is that a lot of galaxy characteristics seem to be affiliated with how massive the central black hole is. We can only measure the motion of stars and gas near the center of nearby galaxies, but some of these other characteristics can be seen in galaxies much farther away. If we can get good measurements in different ways for nearby galaxies, we can use that to bootstrap our measurements for the more distant ones.

Also, NGC 1097 is a barred spiral galaxy, and for various reasons these can be very difficult beasts to observe and get the mass of their black holes. These new results should help resolve some of those issues.

So there you go. If you want to take the measure of a black hole, you have to see how things behave nearby it. That’s probably good advice for many things in life, but nothing more so than the heftiest single objects in the Universe.

Video Advertisement

June 28 2015 11:57 AM

Uncrewed SpaceX Falcon 9 Rocket Explodes After Launch

A SpaceX Falcon 9 rocket carrying supplies to the International Space Station exploded about 2 minutes and 20 seconds after launch Sunday morning. No people were onboard; it was an uncrewed resupply mission. The cause is not yet known.

Here is video of the event (launch is at 51:48, the explosion at 54:05):


SpaceX has not released details yet; a press conference is scheduled for no earlier than 12:30 EDT. I’ll update here when I know more.

Looking at the video, the explosion doesn’t release flames, but instead you see a vaporous white cloud blow away. My guess—and I’m no expert—is that this was a pressurized cryogenic tank failure of some kind. But again, we’ll know more very soon.

Update 1, June 28, 2015 at 16:10 UTC: SpaceX CEO Elon Musk just tweeted that it looks like a tank overpressurization event, as I had guessed:

We should know more soon.

Update 2, June 28, 2015 at 17:25 UTC: At the news conference, SpaceX President Gwynne Shotwell noted that first stage flight went well, and the problem that led to the loss of the vehicle lay elsewhere. They have telemetry from the Dragon capsule from the event, and they are investigating it.

I cannot be sure, but I think this may be the Dragon capsule falling away after the mishap.

Photo by NASA/SpaceX, from the video

Also, I think you can see the Dragon capsule falling away seconds after the explosion. This is a screen grab from a YouTube video, taken at the 54:09 mark. It’s about the right shape, and it’s not too much to think it would survive the destruction of the upper stage. SpaceX hasn’t said, so this is in no way official, but I’m speculating again that there was a tank rupture as per Musk’s earlier tweet. This would’ve led to a big blowout of gas, which caused the vapor cloud. Then the pressure of the rocket’s flight through the air led to the catastrophic collapse of the upper stage. Dragon may have just fallen away after that. It’s also possible the range officer exploded the rocket after seeing the problem. We’ll know more soon. But again, this is guesswork on my part.

The Dragon capsule on top of the rocket had food and supplies for the astronauts on ISS. The three astronauts on board have enough food to last for many months, so they should be OK for now. Also on board the Dragon was an adapter ring for the ISS that would allow future commercial vehicles easier docking access.

This is the first SpaceX failure since it began resupply missions to ISS, but the third overall failure to ISS, including the loss of a Progress vehicle in April and the Orbital Antares rocket in October of 2014. This comes at a time when the Senate has been trying (wrongly, in my opinion) to cut back on funding for SpaceX and other commercial companies, so I expect we'll see statements from those senators on this event shortly. Read them with a grain of salt. Again, we'll know more shortly. Stay tuned.

Correction, June 28, 2015, at 17:50 UTC: I originally misspelled Gwynne Shotwell's first name.

June 28 2015 7:00 AM

California May Make It Harder to Opt Out of Getting Vaccinated. I’m OK With That.

California may be about to pass a law that only allows parents to opt their public school–attending children out of vaccines for medical reasons. Personal or religious objections will no longer be accepted.

This bill, SB-277, has been approved by the state Assembly, and is going to the desk of Gov. Jerry Brown to be signed or vetoed. It’s hard to say what he will do, as he can be unpredictable.


I’m writing this to urge him to sign it. I support this bill.

While this issue can be subtle, when all is said and done, I support mandatory vaccines for public school children. I’ve been pretty clear about it:

If you want to rely on the public trust then you have an obligation to the public trust as well, and part of that obligation is not sending your child to a place with other children if they aren’t immunized against preventable, communicable diseases.

Some people want to claim religious exemption from getting vaccinations, but I don’t find this argument compelling:

I do understand that people might have a religious belief against vaccinations. However, I think religious exemptions can and should only go so far. Certainly they stop dead when religion impinges on my rights to have my child attend a school that is safe. 

By the by, there are very few religions that preach against vaccination (one exception: the Dutch Reformed Church, and there was a major measles outbreak in one of their communities in the Netherlands in 2013). The idea of a religious exemption is, to me, something of a non-issue. But, in the end, I don’t think there should be a religious exemption, either.

Certainly there should be some medical exemptions; some children are allergic to some of the ingredients in vaccines, for example. But these too are relatively rare.

When it comes to refusing vaccines, the largest group is obviously composed of people who think vaccines are somehow harmful, or that mandatory vaccination is taking away their rights.

For those opposing it because they think vaccines are unsafe, well, they’re just wrong. There’s no delicate way to put that, no cushioning it. The claims of health concerns from anti-vaxxers are long, but completely unfounded. Vaccines don’t cause autism. Andrew Wakefield, whose research is the very basis of the modern anti-vax movement, has been called a fraud, has been shown to be guilty of scientific misconduct, shown to have had a massive conflict of interest in his study, shown to have acted unethically, and simply shown to have been wrong. I mean, sheesh.

Vaccines don’t have toxins in them at anywhere near the levels needed to cause problems (as doctors say, dose makes the toxin). Vaccines are effective, their benefits vastly outweigh any small risk, and they are a medical triumph.

For those opposing the bill because they are concerned about parental rights, that’s understandable, but limiting parents’ rights is in some cases justified, especially for the child’s health or for the public welfare. In fact, your rights already are limited. As one obvious example, you can’t drive your child around in a car without them in a safety seat if they’re young, or without wearing a seat belt for older kids. Heck, the state has the right to take your child away from you if you are obviously endangering, neglecting, or abusing them … a sad necessity, but a necessity all the same.

If you don’t vaccinate your child, and there is not a medical reason for it, then you are needlessly endangering your child. It’s really that simple.

And it’s worse even than that. You’re also endangering every child who goes to school with your child.

There are a lot of horrid diseases with devastating health effects that we can stop dead in their tracks with vaccinations. Yet we see outbreaks of them all the time in America, and in many cases it’s because people aren’t vaccinating.

This recent bill in California was spurred by the outbreak of measles that occurred at Disneyland in early 2015. But the need for it is far more broad than that.

Gov. Brown: Please sign that bill into law. You could be saving a lot of children's lives.

June 27 2015 7:30 AM

The Summer Triangle ... Up Close

If you go outside after sunset—and can tear your eyes off of the spectacle of Venus and Jupiter slowly merging in the west—turn around and look to the east. Not long after the sky gets good and dark, you’ll see a trio of bright stars not far above the horizon. Day by day, as summer shambles on,* these stars will be higher in the sky, seemingly strengthening as the season does as well.

This is the iconic Summer Triangle, made up of three of the brightest stars in the sky: Vega, Deneb, and Altair. Straddling the Milky Way, to thousands of amateur astronomers the trio is a sure sign of the season.

I’ve seen countless wide-angle shots of them, placing them in context in the sky, but master-astrophotographer Rogelio Bernal Andreo has done something different; he's taken close-ups of each star, to show what they look like as individuals:

June 26 2015 7:30 AM

What Lurks in the Outer Solar System?

Where does the solar system end?

You might think of the solar system as being the Sun, a bunch of planets*, and various asteroids and comets.


But it’s more complicated than that. Nothing in the Universe ever really has sharp boundaries when you look at it closely. And just because some stuff is big and bright, and other stuff faint and distant, doesn’t mean you can just pick and choose where the city limits lie.

Neptune may be the outermost big planet, but there’s a whole slew of icy objects out past it. And some are way, way past it. And, not surprisingly, they’re weird.

What may be surprising is how much these tiny, distant chunks of frozen water plying the deep black have affected the history of our solar system, and even our very planet. A large fraction of your body is water, and a large fraction of that may have come from the Space Beyond Neptune.

*How many? Oh, roughly a dozen. Maybe fewer.

June 25 2015 3:23 PM

What Is Glittering at Pluto’s North Pole?

As the New Horizons spacecraft nears Pluto, more details are coming into view, and we are beginning to see surface features on the tiny world.

And that means we’ll see things that are … odd. Perhaps “as yet unexplained” is a better term, since we’re seeing these markings for the first time in human history. The press releases have been amazing, but the images released have been enlarged and processed in complex ways to bring out details.


But as the probe gets closer, we can see details without such means. The raw data are posted online within hours of them being transmitted back to Earth, and that means they are available for perusal.

I was looking at a pair of fresh ones taken just today, June 25, at 05:37 UTC (just after midnight, more or less, U.S. time), when New Horizons was just 22.9 million kilometers from Pluto. They’re amazing. Both Pluto and its large moon Charon show all kinds of features, as you can see at the top of this article (the only processing I did was a straight enlargement and a brightness/contrast fiddle). Overall, Charon is much darker than Pluto, but even then surface features are clearly visible.

But that bright spot on Pluto surprised me. That’s near its north pole, and it’s been seen before in earlier images, basically as a splotch. In this image it’s quite obvious.

I wondered if perhaps this was an image artifact, like a particle hit on the detector, but in fact it’s the same in the other image taken 30 seconds earlier. Here are the two shots side by side:

Pictures of Pluto taken at 05:37:30 (left) and 30 seconds earlier (right), enlarged and contrast enhanced.


The spot is very small, probably on the same scale as a single pixel or two in New Horizon’s long-range camera. That means a slight change in the pointing can make its shape look different. Remember too this image is enlarged by a factor of about 10, which can play with the shape as well. While the shape you see may not be real, the brightness contrast is.

But the important thing to note is that it’s seen in both pictures. I’ll note too that Pluto was in a different spot in the camera’s field of view, too, so this isn’t some bad lone pixel either, messing with the shot. This bright spot is quite real. Measuring the pixel brightnesses, it looks to be about twice as bright as the surface around it.

Right now, Pluto is only a couple of dozen pixels across in the long-range camera’s view. New Horizons is moving so rapidly that in 10 days Pluto will be twice this size, and will double again five days after that. Features that are tantalizingly fuzzy now will continue to sharpen, and then we’ll see Pluto as it truly is.

Is this spot at the north pole a fresh impact? Is it nitrogen in its atmosphere freezing out as Pluto slowly moves away from the Sun on its elliptical orbit? Is it one big spot or a lot of little ones (like the weird ones we see on Ceres)?

Give it a couple of weeks. Because that's how close we are. After more than nine years and 5 billion kilometers of travel, New Horizons is about to give us quite a show.

Tip o' the lens cap to Karl Battams for noting new images had arrived.

June 25 2015 12:56 PM

The 2015 Earth and Sky Photography Winners

The good folks at the World at Night—dedicated to preserving the night sky and raising awareness about light pollution—have announced the winners of the sixth annual International Earth and Sky Photo Contest, and as usual they are breathtaking examples of the art of astronomy.

They are all beautiful, and you should see them all, but I particularly liked “The Enchanted Forest” by Lyubov Trifonova (shown at the top of this article). The aurora sweep across the sky, set against snow-covered trees in Russia. The Moon illuminates the scene while the familiar stars of the Pleiades and Taurus hang nearby. This won first place in the “Beauty of the Night Sky” category. You can tell she had to endure some fairly inhospitable circumstances to get that shot.


I was pleased to see frequent BA contributor Brad Goldpaint take second place in this category as well.

All the images have been put into a video for ease of viewing:

The contest is open to people all ages anywhere in the world, a way to show that the sky belongs to all of us. I really do like TWAN and support them; check out their site and see what they do. The photographs they have there are surpassingly lovely and will give you an appreciation of the natural heritage of our night sky.

June 25 2015 7:15 AM

A Star Boils Away Its Own Planet, Turning It Into a Megacomet

Hey, remember last week when I wrote about a Neptune-sized planet (called GJ 436b) that orbits a nearby star, and how it may have an atmosphere that’s almost entirely helium? That’s really weird, since the bigger planets in our solar system have predominantly hydrogen atmospheres. We’ve got nothing like a helium-rich planet in our solar system.

I wrote that the planet seemed to have no methane in its atmosphere as it should; that could be explained by a lack of hydrogen, needed to make methane. Astronomers were guessing that the planet orbits so closely to its star that the lightweight hydrogen would get blown away by the star, and the planet’s gravity is too weak to hold onto it. Helium is heavier and the planet can hold on to it better.


But hang on. It takes a long, long time to strip a planet of hydrogen. Billions of years! So, if what these astronomers were supposing is true, maybe, just maybe, GJ 436b is still losing hydrogen now.

Yeah, about that.

Astronomers using Hubble have just announced that they’ve detected a huge cloud of hydrogen around the planet, and the long, curving tail-like shape to the cloud indicates it’s being blown away from the planet by the star.


When I got the press release for this, I did a double take. You don’t usually get observational proof of an idea so shortly after it’s first announced! But here it is.

GJ 436b
The lack of hydrogen and organic molecules should make GJ 436b a dull gray in color, different than any other planet we've seen.

Artwork by NASA/JPL-Caltech

The planet GJ 436b is called a warm Neptune because, at 23 times the mass of Earth, it’s closer to Neptune's  mass than it is to Earth or Jupiter, and it orbits the star only a few million kilometers out. From our point of view it passes directly in front of the star, transits it, once per orbit. That’s how it was first discovered; once every 2.6 Earth days the starlight dims a bit as it’s blocked by the planet. The amount of visible light blocked is small, less than 1%, but measurable.

The astronomers observed the star, a red dwarf about 30 light years from Earth, before, during, and after such a transit. They used the Space Telescope Imaging Spectrograph (a camera I helped calibrate!) to observe the star in the ultraviolet, where hydrogen atoms just love to absorb light. What they found is that the amount of UV light they saw from the star dropped precipitously, by over 50%, starting about two hours before the transit, and lasting for three hours after.

Not only that, they could measure the velocity of the hydrogen atoms as they move around the star. Using 3D modeling, the best fit to what they see is a huge cloud of hydrogen around the planet, forming a comet-like tail sweeping out behind it. Here's a the video showing a depiction of the planet and cloud passing in front of the star. The graph below it shows how the UV light gets absorbed by the hydrogen over time.

Most likely what’s happening is that the lightweight hydrogen is very hot due to the planet being so close to the star. The atoms move so rapidly due to heat that they get flung far above the planet, where the light from the star can give them an additional push, freeing them from the planet’s gravity. That push isn’t terribly strong, so they don’t just fly off and away, but instead form a puffy cloud around the planet, and a long tail of material trailing the planet as it orbits. That’s much the same as how comets form long curving tails as they orbit the Sun, too. Anyway, that’s why they see a dip in UV before the planet transits (that’s from the puffy cloud) and for many hours after (that’s the tail blocking the light).

The image at the top of this post gives you an idea of what this looks like. The star is boiling away the planet! Well, part of it, at least. Calculating the amount of hydrogen they see, and how fast it’s leaving GJ 436b, it looks like it would take many billions of years for the planet to lose all its hydrogen (though it’s possible the loss rate was higher in the past). But still, the planet is already billions of years old, so this method has clearly caused a severe depletion of hydrogen, explaining the lack of methane in its atmosphere, too.

I love it when a plan comes together.

All in all, this makes me smile. What’s not to love? A giant planet, skimming the surface of its star, its atmosphere being slowly torn away and trailing behind it, leaving behind mostly helium… which, as I mentioned in the earlier post, will make the planet oddly gray in color.

This is nothing at all like any planet we have here in our neighborhood. That’s so cool! The goal of science may be to learn as much as we can about the Universe, but the motivation for so many of us is the weird, the spectacular, the alien, the amazing.

This planet is all of those, and more.

June 24 2015 12:44 PM

Dancing Lights Against the Sky

When you look up in the sky enough, you'll see some really, really weird things. 

YouTube user QuadeM13 was out riding his bike and noticed a strange light beam flashing and twisting around above a cloud. He stopped and took some video of it, and it's, well, really really weird (warning, some NSFW language is muttered therein):


So what is this thing? An alien beacon? Thor going back to Asgard?

Nope. It's ... ice crystals.

Seriously. What's happening here is a wispy cirrus cloud, made up of ice crystals, is being impinged upon from below by a rising cumulus cloud. If the ice crystals in the cirrus are long and needle-shaped, they'll align themselves with the electric field of the lower cumulus cloud, which is generated by up- and downdrafts inside the cumulus cloud. When the electric field suddenly changes (due to, say, lightning discharges inside the cloud), the ice crystals can snap into a different orientation, reflecting and refracting sunlight in a different direction (note that the plume in the video is the same color as the Sun). They do this as a group, making it look like huge coherent structures are suddenly changing shape.

In the video the flare is pretty bright, and I imagine it would be easy to be freaked out by it. I watch clouds a lot and I’ve never seen this, so I doubt it’s terribly common; you need the right circumstances of the cumulus cloud rising into an icy cirrus layer as well as the right geometry to get the sunlight flashing of the crystals.

Back in 2011, I wrote this very odd phenomenon. I had to do some sleuthing to find out what was going on, but what I didn't know at the time is that they're called “crown flashes.” That would’ve made it a lot easier to find out more!

I found a letter to Nature magazine from 1971 describing the phenomenon, so people have been seeing this for a while. A Web search on “crown flash” turns up lots of interesting pictures and videos, too.

The Internet makes finding weird things like this so much easier. I’ve been able to identify iridescent clouds, pileus clouds, and many other weird atmospheric phenomena with just a few clicks. Like any other tool, the ‘Net can be used for ill or for good. I’m glad that it can help us see—and understand—the amazingness all around us all the time.

Tip o’ the Faraday cage to photographer Jerry Lodriguss.