Young star caught eating doughnut!
Dramatic new images show a ring of dust and gas swirling around a newly-formed star. They constitute an exciting first for astronomers as stellar births have proved difficult to catch on film. By astronomical standards they are brief events, occurring in the twinkling of a million years or so, and even worse, stars are born within thick clouds of gas and dust which make it very difficult to get a clear view, even with the most powerful telescopes.
The images on this page show a stellar newborn lying in the constellation of Perseus known to astronomers as LkHa 101. Since its discovery at California's venerable Lick observatory (hence the `Lk' in the name) in the 1950's, this star has been a prime suspect in the hunt for newly-formed massive stars.
The star hid itself well, lying behind clouds of dust so thick that it was almost invisible. Initially its existance was only betrayed by a reflected glow mysteriously lighting up neighboring clouds of dust.
The pictures shown here are the first really close-up view of a stellar birth, as we report in the 22 February, 2001 issue of Nature. Two key technologies were needed to penetrate the dusty veil.
Firstly, the pictures were taken in the infra-red, a type of light which travels more easily through smoke and cloud. This advantage is exploited by military officers viewing battlefields in addition to Astronomers trying to look through dusty nebulae.
The second key advance has been the ability to gain extremely high magnifications with the very latest generation of large telescopes. A technique known as interferometry was used at the Keck Telescope, currently the world's largest telescope. The huge 10m (30ft) mirror was turned into a zoom lens so powerful it could make an image of the head of a pin at a distance of 5 kilometers (3 miles).
What has been discovered in these images is confirmation of an idea which can be traced back two and a half centries to the great German philosopher Immanuel Kant. In 1755 he suggested an intriguing explanation for the orbits of planets in our solar system.
Planets all orbit in the same direction around the sun, their different paths almost all lying in a single flat plane. He suggested this would result if the solar system grew out of a rotating pancake of material. Kant christened this primordial flattened disk an `Urnebel'. At the center, mass is funneled onto the embryonic star, while eddies and clumps circling further out in the disk are the seeds which will grow into planets, moons and asteroids.
What we see in our pictures is just such a circular nebula, one of the first high magnification images of Kant's `Urnebel' just after the star has been formed. The star, which lies at the center of the picture in the darkish hole, has probably stopped sucking material from the disk and is now a fully-fledged luminous star.
Indeed, the star is by now so bright and hot (about five thousand times brighter than our own sun), it has begun to eat away at its own disk. Sculpting with wind and radiation, it has etched a circular cavity within the very material which nourished it.
Despite its high luminosity, a peculiar twist of nature prevents the star from being seen directly in the images. This is because it is very hot (it would appear a searing blue-white to the naked eye), and only emits a small fraction of its energy in the infra-red, where these images were taken. Instead, we see only the hole it has etched in the disk, resulting in the doughnut shape of the images.
But as any child will tell you, it is the hole in the middle of the doughnut that makes it special. This hole is about one billion kilometers across (it would lie between the orbits of Mars and Jupiter if placed in our own solar system). The lopsided appearance is because the disk system is not completely face-on to our line of sight. From our viewpoint on Earth, the disk is tilted towards us in the upper left, which has the effect of dimming the light from that quadrant.
Although structures like this have been predicted, this is the first
image of one still hot and newly-formed.
Already, it is forcing astronomers to rethink their ideas, as the
size of the central cavity is is much larger than earlier calculations
These results are further described in our letter to Nature
"A dusty torus around the luminous young star LkHa 101" by
John Monnier, and
Volume 409, February 22, 2001.
A preprint is available to download if you are interested in learning
about the details of this work.
Nature preprint (postscript)
These links allow you to download and study these images in more detail:
Red false colour image (gif).
Red false colour image (postscript).
Rainbow false colour image (gif).
Rainbow false colour image (postscript).
Greyscale images H/K band (postscript)
Red image, H-band wide field showing binary (postscript).
Photo Credit: Sydney University Physics Department/W.M. Keck Observatory
For further information, see the following sites!
NASA press release on donut around young star
Harvard-Smithsonian Center for Astrophysics
The Research Team:
Peter Tuthill is a reasearcher in the Astronomy Department at the University of Sydney, Australia.
John Monnier works at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
William Danchi is at the NASA Goddard Space Flight Center in Greenbelt, Maryland.
For more information about other exciting research in the field of
stellar interferometry, please see the
SUSI interferometer web page; the
Interferometer Group, at Space Sciences Laboratory, U.C. Berkeley
Telescope Array on Mt Hopkins, Arizona.
This research was supported by grants from the National Science Foundation Stellar Astronomy and Astrophysics Program.
This page was created by Peter Tuthill. For more information, please e-mail: firstname.lastname@example.org