National Astronomical Observatory of Japan



Fomalhaut’s Ring Floating in the Autumn Sky


A Dust Disk Surrounding TW Hydrae

Fomalhaut in the constellation Pisces is famous as the only first magnitude star in the autumn sky. Hubble Space Telescope had previously imaged a dust ring scattering the star’s light. But, by observing the radio waves emitted by the dust, ALMA managed to take a clearer image of the ring. This is a composite image depicting Hubble Space Telescope data in blue and ALMA data in orange. Because the Hubble Space Telescope observes in visible wavelengths, it has to block out a star’s light using a “coronagraph.” ALMA doesn’t have to block out the star light, so it can take clear images without interference from light noise. The radius of the ring is about 20 billion kilometers, about three times the radius of Pluto’s orbit in the Solar System.

Text by: Masaaki Hiramatsu (NAOJ Chile Observatory)

Connecting the Relationship between a Dust Ring and Planetary Formation

When I saw this image, I remembered what I felt looking at Fomalhaut’s half-ring image taken by ALMA which was released several years ago. At that time, I was surprised that we can see almost the same area and resolution as the Hubble Space Telescope. Also, I expected that if the disk could be observed in radio waves, the information showing what molecules are present would allow me to understand the planetary formation environment in more detail. Now that the entire ring has been observed, it is interesting that the components of the dust ring are similar to the comets in the Solar System. This suggests the existence of a standard planet formation process which does not depend on the host star's temperature. This is an important step in understanding planet formation.

Text by: Nobuhiko Kusakabe (NINS Astrobiology Center)
Translation by: Hiroko Tsuzuki and Ramsey Lundock (NAOJ)

Image Data

TelescopeALMA / Hubble Space Telescope
CreditALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF)


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