A Beautiful Image with a Nice Ring To It

Here is a dramatic image of a dying star, courtesy of amateur astronomer and master photographer Robert Gendler. Called the "Ring Nebula," this cloud of of expelled material surrounds a star somewhat like our Sun, but further along in its life cycle.

Usually, regular telescopes only show the inner glowing part that you see in bluish green in the center. But Dr. Gendler has combined the visible-light image with fainter, cooler infra-red information to show how the star has expelled material not just once, but many times. You can see shell after shell surrounding the star. Like a dying man in those old Victorian novels, who coughs and coughs for months before death releases him, this star has been "coughing up" its outermost layers, as it adjusts to the final internal collapse. After the expanding shells have moved away, what will be left is a dense, hot "star corpse" astronomers call a white dwarf.

The image pixels come from the Hubble, Subaru, and Large Binocular Telescopes. By all means click on the picture and look at the larger version.

The Ring Nebula (a favorite astronomical object for newlyweds) is about 2000 lightyears away in the constellation of Lyra. It is perhaps the best known example of a "planetary nebula." (The name comes from their fuzzy appearance in early telescope; the expanding shell of gas has NOTHING to do with planets.) Astronomers also call it M57 (the 57th entry in Charles Messier's catalog of fuzzy objects in the sky.) If you search for M57 on the web you can learn a lot more about it; or just enjoy the weirdly wonderful picture.

Robert Gendler's other astronomy images can be found at: http://www.robgendlerastropics.com/  

To see a larger version of the amazing Hubble Space Telescope image of this object (which is at the center of our picture), go to: http://hubblesite.org/newscenter/archive/releases/2013/13/image/b/format/large_web/ 

Finding an Invisible Star Corpse

An international team of astronomers recently reported a wonderfully strange discovery.  They found the faint, cold "corpse" of a dead star, not by detecting any light from it, but through its gravity grip on another star corpse with which it shares a system.  It's quite a story!

To follow it, we need to take a brief excursion into the gruesome deaths of stars.  All stars collapse at the end of their lives, but stars with different amounts of mass (stuff) die differently.  Less massive stars (like our Sun) eventually die by collapsing into a ball not much bigger than a planet -- such a white-hot but tiny corpse is called a "white dwarf."  They start out as really hot, but cool off as they shine away their light and heat into the darkness of space.

More massive stars have a more complicated death in store for them. They die in a sudden event, where the core of the star collapses catastrophically, while the rest of the star blows up in a giant explosion called a "supernova."  We have discussed such explosion in several posts. 

What interests us today, however, is the tiny core of the star which is super-squozen (that's a technical term!) by the star's death.  It's typically not much bigger than your average suburban town, and called a "neutron star" -- because in it all the atoms lose their identity and become neutrons.

Such a neutron star, surrounded by an "atmosphere" of materials from the messy explosion of the rest of the star, can sometimes be detected by faint pulses of radio waves it gives off, and is then called a "pulsar."  (A watch company "borrowed" that name, but we astronomers had it first.)

So now here's the discovery.  Astronomers using radio telescopes first discovered a pulsar in the constellation Aquarius, indicating that a neutron star was revealing itself to us.  But the pulsar showed signs of wobbling, as if something with strong gravity was orbiting around it and pulling on it.  Careful measurements reveal that the orbiting object is a white dwarf, and it takes only two and a half days to revolve around the neutron star. (Remember that Earth takes 365 days to go around the Sun, so these two star corpses are in an intimately close dance.)

To their amazement, when other astronomers tried to find the light or heat of the white dwarf companion, they COULDN'T -- not even with the biggest telescopes.  That white dwarf must be so old that it has cooled down below the level where we can find it (at its distance of about 900 light years.)  This makes it the coldest, dimmest star corpse ever found.  If you are into star corpses, and we astronomers really are -- this is a big deal.  It's remarkable that with today's technology, we can know this white dwarf is there not by its light, not by its heat, but just by its pull on another dead star nearby. 

Note: Our image is just a painting, not any kind of photograph.  It shows the pulsar on the left (with two beams of radio waves coming from it) and the white dwarf on the right.  Although we can see light coming from the white dwarf in the painting, in real life the star is so faint and far away, no light from it is detectable with today's instruments.

A Triple System of Star Corpses

An international team of astronomers has just reported the discovery of one of the weirdest star systems we have ever seen -- a triple system of star corpses (dead stars) whirling around each other in a space smaller than the Earth's orbit around the Sun.

The system of stars is more than 4,000 light years away, in the constellation of Taurus. (But this story is no bull!) The system doesn't have a name, only a catalog number.  It consists of one "neutron star" (which pulses with radio waves) and two "white dwarfs."  Generally, a tiny "neutron star" only forms after a massive star dies by blowing itself to pieces, leaving a very compressed remnant (or "corpse") behind.  So, those three stars, which show evidence of having formed together, had to remain together even when the biggest star of the three exploded.  Later, the two smaller stars died and also became compressed objects (not much bigger than a planet) called "white dwarfs."  (They get that name because they are small and white hot.)

Now the three corpses continue to spiral around each other, in a strange cosmic ballet .  The heaviest corpse, the "neutron star" is really dense -- it is so compressed that to make something like it on Earth, we would have to take all the people in the world and squeeze them into a raindrop!  (Then we would have one rain-drop sized piece of the neutron star.)

Sometimes we see such "neutron stars" giving off spinning magnetic beams of radio waves.  Whenever such a radio beam sweeps over the Earth, we get a pulse of radio waves.  In such cases, we also call these dead stars "pulsars."   Their beams of energy can be timed with great accuracy.

In 1974, my former college advisor, Joseph Taylor (and Russell Hulse,) discovered the first pulsar in a double star system.  Measuring its pulses enabled them to verify important predictions of Einstein's General Theory of Relativity, and earned them the 1993 Nobel Prize in Physics.  At the time, astronomers thought that finding a neutron star/pulsar with a companion was pretty surprising (although today other double systems are known.)

Now suddenly, we have a neutron star/pulsar with TWO companions.  How completely and wonderfully weird!  And this particular neutron star spins hundreds of times per second. Its fast spin and two companions will allow astronomers to measure the predictions of Einstein's theories even more precisely than we have been able to do in the past.