Bloated Stars Swallow Giant Planets

Larry Klaes (
Thu, 12 Aug 1999 18:32:43 -0400

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>Approved-By: "H. Alan Montgomery" <fhd@LCC.NET>
>Date: Wed, 11 Aug 1999 19:35:33 -0700
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>Subject: Bloated Stars Swallow Giant Planets
>Subject: Bloated Stars Swallow Giant Planets
>Date: 12 Aug 1999 21:23 UT
>From: (Ron Baalke)
>Organization: Jet Propulsion Laboratory
>EMBAROGED UNTIL: 9:00 a.m. (EDT) August 12, 1999
>CONTACT: Ray Villard
> Space Telescope Science Institute, Baltimore, MD
> (Phone: 410-338-4514)
> (E-mail:
> Mario Livio
> Space Telescope Science Institute, Baltimore, MD
> (Phone: 410-338-4439)
> (E-mail:
>The phrase "big fish eat little fish" may hold true when it comes
>to planets and stars.
>Perhaps as many as 100 million of the sun-like stars in our galaxy
>harbor close-orbiting gas giant planets like Jupiter, or stillborn
>stars known as brown dwarfs, which are doomed to be gobbled up by
>their parent stars.
>Space Telescope Science Institute astronomer Mario Livio and
>postdoctoral fellow Lionel Siess did not directly observe the
>planets, because they had already been swallowed by their
>parent stars.
>But Livio did find significant telltale evidence that some giant
>stars once possessed giant planets that were then swallowed up.
>The devouring stars release excessive amounts of infrared light,
>spin rapidly, and are polluted with the element lithium.

>About 4 to 8 percent of the stars in our galaxy display these
>characteristics, according to Livio and Siess. This is
>consistent with estimates of close orbiting giant planets, based
>on discoveries of extrasolar planets by radial velocity
>observations, which measure the amount of wobble in a star due
>to the gravitational tug of an unseen companion.
>An aging solar-type star will expand to a red giant and in the
>process engulf any close-orbiting planets. If the planets are
>the mass of Jupiter, or greater, they will have a profound
>effect on the red giant's evolution.
>First, according to Livio's calculations, such a star is bigger
>and brighter because it absorbs gravitational energy from the
>orbiting companion. This heats the star so that it puffs off
>expanding shells of dust, which radiate excessive amounts of
>infrared light.

>The orbiting planet also transfers angular momentum to the star,
>causing it to "spin up" to a much faster rate than it would
>normally have. Giant planets carry the lion's share of angular
>momentum in a stellar system. For example, Jupiter and Saturn
>contain 98 percent of the angular momentum in the solar system.
>Finally, a chemical tracer is the element lithium, which is
>normally destroyed inside stars. A newly devoured Jovian planet
>would provide a fresh supply of lithium to the star, and this
>shows up as an anomalous excess in the star's spectrum.
>In our solar system Jupiter is too far from the Sun to be
>swallowed up when the Sun expands to a red giant in about
>5 billion years. However, detections of extrasolar planets
>do show that Jupiter-sized planets can orbit unexpectedly
>close to their parent stars. Some are even closer than Earth
>is to our Sun. These worlds are doomed to be eventually
>swallowed and incinerated.
>The Space Telescope Science Institute is operated by the
>Association of Universities for Research in Astronomy, Inc.
>for NASA, under contract with NASA's Goddard Space Flight
>Center, Greenbelt, MD. The Hubble Space Telescope is a
>project of international cooperation between NASA and the
>European Space Agency.
>- end -
>NOTE TO EDITORS: An illustration associated with this release
>is available on the Internet at: