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 hot blue star, which lies at the center of the hole in the doughnut, 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.

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 suggest. These results are further described in our letter to Nature "A dusty torus around the luminous young star LkHa 101" by Peter Tuthill, John Monnier and William Danchi 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)
Nature preprint (PDF)

As seen on TV! Movie (mpeg1) of a nationally-aired newscast (Australia's SBS TV) from February 2001 talking about the new images.
Click Here for a fairly large (18 megabyte) movie file.
If this is too large, Click Here for a smaller (9 megabyte) version with significantly lower image quality.

Earlier pictures on this web page (and the thumbnails at the top) show only the doughnut without the star. We have since improved our analysis so that the star is now visible in the pictures, however it is important to point out that these images are made at the very limit of the telescope's theoretical resolution. Higher resolutions still will be required to truly image this system without ambiguity.

These links allow you to download and study these images in more detail:
  Red/Blue false colour image with star (jpg).
  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 School of Physics at the University of Sydney, Australia.
John Monnier works at the University of Michigan Physics Dept
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 Infrared Spatial Interferometer Group, at Space Sciences Laboratory, U.C. Berkeley or the Infrared Optical Telescpe Array on Mt Hopkins, Arizona.

This research was supported by grants from the Australian Research Council and the US National Science Foundation Stellar Astronomy and Astrophysics Program.

For more information, contact:
Dr Peter Tuthill
Astronomy Department
School of Physics, University of Sydney
email: p.tuthill -at-