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.
In 2012, during a weekend astronomy event (called SETICon II), I had the pleasure and privilege of doing a 45-minute on-stage interview with Frank Drake, the distinguished astronomer who did the first scientific experiment searching for evidence of intelligent life among the stars. The interview was videotaped at the time, but not released.
Now, to celebrate the beginning of the 30th year of the SETI Institute (the organization engaged in continuing that search), they have released the interview on YouTube and you can see it at:
http://www.youtube.com/watch?v=HPQz-kdaxNo
Dr. Drake was the first President of the SETI Institute, and I have been a board member there since the beginning. We discuss both his career and his current thinking about the search, including his current view of the Drake Equation (a way of estimating the chances of intelligent life out there). He also reflects on a number of modern developments, including the discovery of numerous planets orbiting other stars and novel ways of searching for extra-terrestrial civilizations.
For more about the non-profit Institute, you can explore their web site at: www.seti.org
An international team of astronomers has found a new kind of astronomical event in the universe -- a powerful flash of radio waves, lasting only a few thousandth of a second, but coming from vast distances away.
Radio waves -- the same kind of invisible "wireless waves" that bring news of traffic jams to our car radios or wifi for our laptop computers -- come from a variety of natural events in the cosmos. If your car radio were to convert them to sound waves, they would sound like static. Radio static comes to us from the magnetic regions of the Sun and Jupiter, from remnants of exploded stars, and many other sources in the sky. But the "transmissions" usually last a long time.
A sudden burst of such waves lasting only a few thousandth of a second (and then never again) came as a surprise to astronomers. The first of these was discovered six years ago, but was classified as doubtful until others could be found. Now astronomers have found a total of five from different directions in the sky. Indications are that they come from far away -- from far beyond our Milky Way Galaxy. If so, and we can still detect them from Earth, they must be very strong bursts indeed. (In the same way, if you scan the horizon and see a flash of light from a distant city, whatever made the light must be quite bright to cross the space between cities and still be visible to your eyes.)
What could make such brief, super-strong bursts of radio waves? It must be something small and powerful. First candidates include the collapsed corpses of stars that are called neutron stars. These are what remains of stars that exploded long ago, and they can pack more than a Sun's worth of material into a ball no bigger than a suburban town (about 20 miles across!) When such densely packed star corpses collapse further or have a magnetic hiccup, they can give off a quick shot of radio energy.
But at this point, no one really knows what sorts of cosmic objects the radio bursts come from and we are eagerly searching for more. This situation is very similar to what happened in 1967 with another kind of invisible wave, called gamma rays. A secret spy satellite found a few bursts of gamma rays coming from space. At first, no one could figure our what they were and why we saw them randomly around the sky. But as decades passed, and we detected more and more of them, with better and better instruments, we learned a lot more about them and began to come up with really good explanations for these "gamma-ray bursts." We may be at the beginning of a similar era of further exploration and gradual explanation with these radio bursts. As they say on the radio, "stay tuned."
(The artistic image with this post shows the radio telescope in Australia that found the new bursts, together with a blue dot symbolizing the (invisible) burst, some distance away from a map of radio waves coming from our own Milky Way, shown with reddish colors. So only the color of the telescope is real, the other colors try to show things our eyes cannot see, using colors we can see. But how else can we have a nice picture with the story?)
