Transcript Hungry Young Stars: A New Explanation for the FU Ori Outbursts

Hungry Young Stars: A New
Explanation for the FU Ori
Outbursts
Shantanu Basu, Eduard I. Vorobyov
Department of Physics and Astronomy
The University of Western Ontario
207th AAS Meeting, January 11, 2006
Computer Simulations of Star Formation
Our calculations reveal the explanation for colossal bursts of
luminosity in young stars. This explains the remarkable
transient brightening (by factors of hundreds) of a class of
young stars known as the FUOr’s.
• We solve the equations of gas dynamics
including the effect of a surrounding
nebular cloud that feeds a gas disk and
protostar (central yellow circle in image).
Black region contains low-density
nebular material
protoplanetary embryo
• The gas disk forms spiral arms and
protoplanetary embryos (see arrows).
• Interactions with the spiral arms in the
disk drives the embryos into the central
star, resulting in colossal bursts of
luminosity. This process repeats as long as
nebular material rains onto the disk.
The FU Ori phenomenon
The Orion Constellation
FU Ori – 30 NW of Betelgeuse,
the prototype for a class of stars
Betelgeuse (a Ori)
Orion Nebula (M42)
Rigel (b Ori)
Negative image – C. Briceno
FU Ori brightened by a factor of ~ 250 in the course of one year, and is
currently declining in brightness with a decay timescale of 50-100 years.
The surrounding material reveals that this is an infant star. It is believed
that all young stars undergo multiple eruptions.
Disk Evolution
and Stellar Mass
Accumulation
Image of gas
density in a disk
surrounding a
new protostar.
Rate at which
mass falls onto
the protostar.
E. I. Vorobyov & S. Basu
Spiral Arms  Embryos  Luminosity Bursts
Luminous bursts due to episodes of embryo consumption
At the peak of the outburst, the star
is at least several hundred times
more luminous than our Sun.
The star devours the equivalent of
one Earth mass every ten days
during the century-long outburst.
E. I. Vorobyov & S. Basu
Summary
• We provide an explanation for the origin of FU Ori bursts.
• A young star devours embryos that form in the disk, resulting in colossal
bursts of luminosity. This process repeats as long as nebular material rains
onto the disk.
• The new feature in our model is the self-consistent formation and evolution
of a gas disk due to matter falling in from the surrounding nebula.
• The last generation of embryos (formed when nebular gas is gone) may
escape consumption and form giant planets, brown dwarfs, or companion
stars, depending on their mass. Future calculations will reveal the answer.
All press conference materials can be downloaded from
www.astro.uwo.ca/~basu/aas207. Some CD’s are available upon request.
This research has been performed by Dr. Eduard I. Vorobyov and Prof. Shantanu Basu
of The University of Western Ontario, and funded by the Natural Sciences and
Engineering Research Council of Canada, the North Atlantic Treaty Organization, and
the Canadian Institute for Theoretical Astrophysics.