Sunday, August 30, 2015

Two Giant Black Holes Whirl at the Core of an Active Galaxy


Using the Hubble Space Telescope, a team of astronomers has found that a superbright (active) galaxy is powered at its core by two supermassive black holes whirling around each other in only a bit more than one year. This remarkable galaxy is called Markarian 231, after the Armenian astronomer who made a catalog of such active galaxies (with unusually bright centers.)
The galaxy is almost 600 million lightyears away, so we cannot see the tiny area in the center which contains the black holes directly. But a detailed study of the ultraviolet light from the core of the galaxy strongly implies that a black hole containing enough material to make 4 million Suns is whirling around a much larger black hole (with mass inside for 150 million Suns.)
Think about those numbers! You would not want to live near such overweight black holes, but luckily they are confined to the central regions of galaxies (including our own Milky Way) and are not a feature of the galactic outskirts where our solar system resides in comparative peace.
The idea that enormous black holes like this can share the same environment is not news to astronomers, but it's nice to have such a clear example. We now know that the giant islands of stars called galaxies probably all started much smaller and have been growing through "mergers" (if you'll pardon our appropriating a word from the world of business.)
Smaller galaxies are "eaten" by larger ones, or two galaxies of equal size are attracted together by their mutual gravity. If the smaller galaxies each contain a big black hole, both black holes will wind up near the center of the merged object. If the original galaxies had orbiting motion around each other, their inner black holes will have some of that motion, and can circle each other until -- later -- their gravity also pulls them together.
The fact that the two black holes in Markarian 231 take only about one year to go around means they will collide in a few hundred thousand years (a long time compared to the presidential nomination season, but short for galaxies.)
When two black holes collide you get -- surprise, surprise -- a bigger black hole. But we have caught Markarian 231 in the act of a small galaxy having been swallowed, but before the two black holes had time to merge. There are stars and huge clouds of gas and dust being pulled in by the pair of black holes and as they are torn apart and whirled around, they give off a lot of energy.
It's that energy of doomed material (before it falls into one or the other black hole) that makes Markarian 231's center so unusually bright.
The method used to find the waltzing, whirling black holes in this galaxy holds promise for finding other pairs of giant black holes in other distant galaxies. And the existence of such pairs of hungry black holes is good evidence that our merger theory of how galaxies "bulk up" is correct.

(By the way, our image, above, is a painting, based on the Hubble data.  As we said, we can't take a picture of the inner part of the galaxy.  But below is a Hubble image of the entire disturbed galaxy with its bright center.)


Sunday, August 9, 2015

Good Meteor Shower This Wednesday Night


This Wednesday evening and Thursday morning there will be one of the best meteor showers you and your family can see.

This is a great year for the Perseid meteor shower, because it is happening during the phase of the Moon called New Moon (which is when the moon is absent from the sky).  So there will be no moonlight to interfere with seeing the faint “shooting stars” of the meteor shower.

The best night is the evening of Wed, Aug. 12 and morning of Thur., Aug. 13, although there could be significantly more meteors on the night before and the night after too.  Meteors (which have nothing to do with stars) are pieces of cosmic dust and dirt hitting the Earth’s atmosphere at high speed and making a flash of light.

The peak of the shower is predicted to happen around 1 am PDT Aug. 13th, which means that after it gets dark on Aug. 12th, there should already a good number of meteors to watch for.

Here are a few tips for best viewing:

8 HINTS FOR TAKING A METEOR SHOWER

1. Get away from city lights and find a location that’s relatively dark
2. If it’s significantly foggy or cloudy, you’re out of luck
3. Your location should allow you to see as much of the dome of the sky as possible
4. Allow time for your eyes to get adapted to the dark (at least 10 -15 minutes)
5. Don’t use a telescope or binoculars – they restrict your view (so you don’t have to be part of the 1% with fancy equipment to see it; this is a show for the 99%!)
6. Dress warm – it can get cooler at night even in August
7. Be patient (it’s not fireworks): keep looking up & around & you’ll see flashes of light
8. Take someone with you with whom you like to spend time in the dark!

The Perseid meteors are cosmic “garbage” (dust and dirt clumps) left over from a regularly returning comet, called Swift-Tuttle (after the two astronomers who first discovered it).  The comet itself returns to the inner solar system every 130 years; it was last here in 1992.  During each pass it leaves dirt and dust behind and it is this long dirt and dust stream that we encounter every August.  Some experts are predicting we might briefly encounter an especially crowded part of the debris stream this time.


Each flash you see is a bit of material from the comet hitting the Earth’s atmosphere and getting heated up (and heating up the air around it) as it speeds through our thick atmosphere.  Both the superheated dust and dirt and the heated air contribute to the visible light we observe.  Since comets are left-overs from the early days of our solar system, you can tell yourself (or your kids) that each flash of light is the “last gasp” of cosmic material that formed some 5 billion years ago.

[Note: image from Mike Hanley, American Meteor Society]

Sunday, July 26, 2015

New Pluto Images Reveal Glaciers Flowing from the Heart


New images released from the New Horizons spacecraft's encounter with Pluto reveal a reddish world, where water is as hard as rock, and substances that are gas on Earth have become ice glaciers. The beautiful color picture with this post shows you a section of Pluto that includes the heart-shaped feature named after Clyde Tombaugh, Pluto's discoverer. The left lobe (section) of the heart is being called the "Sputnik region," after the first satellite humanity ever sent into outer space.
Why is Pluto reddish? The team's first thought is that ultra-violet light from the Sun acts on the gases in the thin Pluto atmosphere -- methane (natural gas) in particular -- and breaks them apart and reforms them into more complicated combinations of hydrogen and carbon. Eventually, the molecules get so complex and heavy, they fall out of the air and coat the surface. Such hydrocarbons tend to be reddish when we see them on other worlds.
The New Horizons craft has only returned about 5% of the data it has stored in its memory, but even first results show haze layers in the Pluto atmosphere that support the notion of the air having chemical reactions going on, despite the cold.
If you look at the Heart in the picture, you can see that the left Sputnik region (which is about the size of Texas) has a thicker covering of ice than the right half of the Heart. Our black-and-white image shows a close-up about 250 miles wide in the northern part of Sputnik. At the top you see some of the older, cratered terrain that is above the Heart. But below that, the Heart itself is smooth and young-looking (no craters, which are a sign of age.)


The smooth ice we see is made of nitrogen, methane, and carbon monoxide, its top layers freezing out of the air when Pluto gets further from the Sun. (Pluto was closest to the Sun in its almost 250-year orbit in 1989, so we are just moving away from the time that Pluto is warmest.)
At Pluto temperatures, an ice made of nitrogen will very slowly flow, like a glacier flows across the landscape on Earth. The arrows on our black-and-white image show the direction scientists think the ice is flowing in Sputnik. At Friday's press conference, the experts said that their impression of Sputnik is that it's a very young region (geologically speaking) -- perhaps only tens of millions of years old. (For comparison, we think Pluto, like the rest of the solar system, is 4600 million years old.) Its glaciers have moved into any available regions next to Sputnik, and have filled valleys and craters on all sides.
Look also at the intriguing "polygon" patterns (many-sided figures) in the ice of Sputnik on our picture. They look like huge, geometric cells in the ice, perhaps half a mile or more deep. One possibility is that in these cells, hotter material from deeper inside is slowly rising, a process called "convection."
These images and ideas are just the (pardon the expression when discussing Pluto), just the tip of the iceberg. It will take 16 months for the full set of pictures and data to be sent back from New Horizons. Better images are expected in September, for example. Stay tuned.


In this last image, you see Pluto (left) and its large moon Charon in realistic color.  Such a dramatic pair at the outskirts of our solar system!

Friday, July 17, 2015

Getting Close-up with Pluto's Moon Charon


One of the most intriguing things about Pluto is that it is more of a double planet than a planet with moons. One of Pluto's moons, Charon (pronounced like Sharon or Karen; both are used) is half the size of Pluto. No other moon we know is this big compared to the planet it orbits -- just another way that the Pluto system operates outside the usual rulebooks.

The diameter of Charon has been measured to be 751 miles, about the size of Texas. Charon has settled into the most comfortable orbit around Pluto that nature permits. It rotates and revolves in 6.4 Earth days, which is also the rate at which Pluto turns. This means that the day on Pluto is the same length as the Charon month, which hurts your head if you try to think too much about it.

Now the New Horizons craft is starting to send back images of Charon as well, and again, we are surprised. Our photo shows a black and white global picture of Charon that has been tinted with actual color information from one of the other instruments. The New Horizons team is informally referring to the striking dark spot near the top of the image as "Mordor," much to the delight of fans of the Lord of the Rings trilogy.

But the inset in our picture is the most interesting. It shows an area of about 240 miles across (from top to bottom) and you can see some of the trenches and canyons that we are finding on Charon. Craters are also visible. Near the top left, we see a giant ice mountain sticking out of a trench. The NASA news release says: “This is a feature that has geologists stunned and stumped.” How did the mountain get or grow in there? It's those kind of odd mysteries that scientists live for.

(By the way, if you were asking yourself why the big moon has two different ways of pronouncing its name, it's a romantic story. The proper pronunciation from Greek mythology is like "Karen". But James Christy, the astronomer who discovered the big moon in 1978, secretly wanted the name to also remind people of his wife Charlene. So he likes making the name sound more like "Sharon." Astronomers (like most people) love romantic stories, so many use the pronunciation that Christy likes.

And Pluto itself has a name with a secret -- the astronomers at the Lowell observatory wanted to name it after their patron and founder, Percival Lowell, but we don't name planets after real people. So when a schoolgirl in England suggested the name Pluto to them, they jumped at it, since the first two letters are Lowell's initials.)

Wednesday, July 15, 2015

First Close-up Peek at Pluto's Surface


Here is the first detailed image of the surface of Pluto, released today, and it's already providing surprises. The yellow bar gives you a sense of scale; Pluto's diameter is 1473 miles (just measured by New Horizons), so we are seeing only a small part of it here.
The angular structures in the top half of the picture are mountains, the tallest being about 2 miles high. Most likely these mountains are made of frozen water -- it's so cold on Pluto that water becomes harder than rock. In fact, it is likely to be layers of "hard frozen water" that make up much of the surface of this distant world.
The biggest surprise is that the surface shows no craters, large or small. Craters are made on every world when chunks of rock or ice hit and carve out a circular depression. Since every world is regularly being hit by pieces of cosmic debris that fly through our solar system, any world without craters must have a way of erasing them pretty quickly after they form. Scientists are estimating that the absence of craters means that the surface of Pluto is being refreshed by some process, and can't be more than a hundred millions years old -- which is very YOUNG compared to the 4600 million year age of the solar system. What keeps the surface of this little world refreshed and erased is the first challenge Pluto has thrown in the face of the scientists eager to study it.

Sunday, July 12, 2015

The Revenge of the Dwarf Planets

Pluto Seen July 11, 2015 from NASA's New Horizons Spacecraft

This coming Tuesday, July 14th, humanity will -- for the first time -- fly by the world formerly known as planet Pluto.  Actually, the New Horizons spacecraft will be flying by a double world, because Pluto has a giant moon, Charon, which is half its size.  I can't wait to see the pictures.

In fact, see the Pluto image with this post -- it's from yesterday and already shows intriguing spots and circular areas.  Check out the even better new pictures and information as they are revealed this coming week and month.  You can find them at: http://pluto.jhuapl.edu/ 

When the data from the flyby are returned to Earth -- and they will take a year to download (and you think your connection is slow!!) -- we will have completed our first-look exploration of all the main worlds known when most of my readers were born.

Pluto was "kicked out of the planet club" only because a whole bunch of other "Plutos" were found beyond Neptune.  Pluto turned out to be the first of its kind (found by Clyde Tombaugh at Lowell Observatory in 1930), but now we've found Eris (which is the same size as Pluto) and several other round icy worlds that are smaller versions of them.  We probably should have picked a less insulting name than dwarf planet, but we used the word dwarf successfully in combination with star and galaxy, so we didn't anticipate so much public hostility to it.  For the full story, see: http://www.pbs.org/seeinginthedark/astronomy-topics/planets-and-pluto.html 

A few of Clyde Tombaugh's ashes are aboard the New Horizons craft.  You can read his own story of the discovery at: http://astrosociety.org/wp-content/uploads/2013/02/ab2009-23.pdf




Here is Clyde Tombaugh with your friendly blogger in 1985

Pluto is known to have four smaller moons, and others may yet be discovered in the coming weeks.  Pluto also has a thin changeable atmosphere, which instruments will be investigating as we fly by.

Another world that got reclassified in the Pluto saga was Ceres, the largest asteroid, which is now also called a dwarf planet.  Ceres is the only member of the asteroid belt between Mars and Jupiter to be round.  The Dawn spacecraft is settling into a lower and lower orbit around Ceres this summer and fall, and will be sending back never-before-seen details of what this intriguing world (about the size of Texas) looks like.

So it's going to be a summer of dwarf planet discovery.  They are going to be in the news so much, maybe we'll forget the issue of the name and enjoy them for what they have to tell us about the history and diversity of the solar system.

If you are really into the Pluto encounter, the most comprehensive post about what's happening is Emily Lakdawalla's at: http://www.planetary.org/blogs/emily-lakdawalla/2015/06240556-what-to-expect-new-horizons-pluto.html 

Wednesday, June 17, 2015

Astronomers Find a Planet Like Mars in a Distant Star System


A team of astronomers has found the equivalent to planet Mars in a star system with three planets 200 light years away.  This is the planet with the lowest mass found so far around any normal star.  That’s because the methods that allow us to find the masses of planets (how much they weigh) generally work best for planets that are heavier.  Here a wonderful combination of circumstances allowed the team (including Jason Rowe of the SETI Institute) to make their record-breaking measurement.

The nameless star system is given the catalog designation Kepler 138, because the three planets, orbiting a cooler star, were first discovered by the Kepler spacecraft.  Kepler allows astronomers to find planets when they move across the face of their stars, causing a tiny eclipse (or “transit.”)  Tremendously accurate instruments aboard Kepler measured the decrease of light when each planet got in front of the star.

The three planets are each closer to their star than Mercury is to our Sun.  The planet that resembles Mars, closest of the three, takes only 10.3 days to go around.  In other words, a year on that planet is 10 Earth days.  Think how often you’d have to celebrate annual events, like your birthday!

The present team of astronomers (which also includes members from NASA’s Ames Research Center and Penn State) followed the three planets’ transits over time and noticed that they did not occur at the same time each orbit, because the gravity of the other two close planets was tugging on each one.  By measuring the size of the tugs, the astronomers could derive the gravity (mass) of each planet, something that is otherwise very hard to do.

Now here is the clever part.  When we watch a planet go in front of its star, that allows to measure how big the planet is (its diameter).  Bigger planets block more light.   So for these three planets, we now had the mass (from the tugs) and the size (from the transits).  Most of the time, when they find planets around other stars, astronomers only have one OR the other. 

Since we have both in this case, that allows us to calculate the density of each world. If a planet is dense, it is likely to made mostly of rock, like Earth is.  If a planet is not so dense, it combines rock with ice or even perhaps melted ice, such as the liquids we find inside Jupiter and the other partly liquid planets in our solar system.

This is what allowed the team to say with some certainty that the inner planet in the Kepler 138 system is about the size of Mars and about the same composition as Mars.  The planet is roughly 10% the mass of Earth and half the size of Earth, just like Mars is.   This is the smallest world for which we have both size and mass.


Almost 2000 planets are now known around other stars, a remarkable number, given that the first one was discovered just 20 years ago.  What amazes us is the variety of planets out there.   There are huge planets, bigger than Jupiter, but orbiting very close to their stars.  There are planets we are calling super-Earths, that are intermediate in size between Earth and Neptune.  And now we know that there are smaller, solid worlds like Mars.  Some smaller worlds are really close to their stars, like the one around Kepler 138, but others are much further out, like Mars is in our solar system.   Nature likes diversity in astronomical settings, much as she likes it for people.

(For a nice "infographic" about the Kepler 138 system compared with our solar system, see: