Using the Subaru Telescope and the NASA/ESA Hubble Space Telescope, astronomers have found evidence for a Jupiter-like protoplanet around the young star AB Aurigae orbiting at a wide separation (93 AU).
Currie et al. were able to directly image AB Aurigae b over a 13-year span using Hubble’s Space Telescope Imaging Spectrograph (STIS) and its Near Infrared Camera and Multi-Object Spectrograph (NICMOS). In the top right, Hubble’s NICMOS image captured in 2007 shows AB Aurigae b in a due south position compared to its host star, which is covered by the instrument’s coronagraph. The image captured in 2021 by STIS shows the protoplanet has moved in a counterclockwise motion over time. Image credit: NASA / ESA / Thayne Currie, Subaru Telescope & Eureka Scientific Inc. / Alyssa Pagan, STScI.
AB Aurigae is a very young star located approximately 531 light-years away in the constellation of Auriga.
Also known as HD 31293, HIC 22910 and SAO 57506, the star is a member of the 1-3-million-year-old Taurus-Auriga star-forming region.
The newly-discovered exoplanet, named AB Aurigae b, is embedded in a protoplanetary disk of dust and gas with distinct spiral structure swirling around AB Aurigae.
“Nature is clever; it can produce planets in a range of different ways,” said Dr. Thayne Currie, an astronomer with the National Astronomical Observatory of Japan, NASA’s Ames Research Center, and Eureka Scientific Inc.
“All planets are made from material that originated in a circumstellar disk.”
“The dominant theory for Jovian planet formation is called core accretion, a bottom-up approach where planets embedded in the disk grow from small objects colliding and sticking together as they orbit a star. This core then slowly accumulates gas from the disk.”
“In contrast, the disk instability approach is a top-down model where as a massive disk around a star cools, gravity causes the disk to rapidly break up into one or more planet-mass fragments.”
AB Aurigae b is about 9 times more massive than Jupiter and orbits its host star at a whopping distance of 93 AU — over two times farther than Pluto is from our Sun.
At that distance it would take a very long time, if ever, for a Jupiter-sized planet to form by core accretion.
This leads the astronomers to conclude that the disk instability has enabled this planet to form at such a great distance.
And, it is in a striking contrast to expectations of planet formation by the widely accepted core accretion model.
“This new discovery is strong evidence that some gas giant planets can form by the disk instability mechanism,” said Dr. Alan Boss, an astronomer with the Carnegie Institution of Science.
“In the end, gravity is all that counts, as the leftovers of the star-formation process will end up being pulled together by gravity to form planets, one way or the other.”
The discovery is reported in a paper published this week in the journal Nature Astronomy.
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T. Currie et al. Images of embedded Jovian planet formation at a wide separation around AB Aurigae. Nat Astron, published online April 4, 2022; doi: 10.1038/s41550-022-01634-x
