Astronomers using the NASA/ESA Hubble Space Telescope have spotted a massive dust structure — about 150 billion miles across — around HR 4796A, a young star located 220 light-years away in the southern constellation of Centaurus.
The vast, complex dust structure, about 150 billion miles across, envelopes the young star HR 4796A. Image credit: NASA / ESA / G. Schneider, Universe of Arizona.
HR 4796A, a member of a binary star system, is about 1.7 times larger than the Sun, 23 times more luminous, and approximately 8 million years old.
This star first drew attention in 1991 when Michael Jura from the University of California, Los Angeles reported an unusual amount of dust surrounding it, based on observations made by NASA’s Infrared Astronomical Satellite in 1984.
In 1998, a team led by University of Pennsylvania astronomer David Koerner announced ground-based thermal infrared data indicating that the dust around HR 4796A is in the form of a disk. However, the data lacked the resolution to precisely define the geometry of the disk.
A year later, Brad Smith from the University of Hawaii and colleagues found that HR 4796A is actually surrounded by a bright and narrow ring of dust, located about 6.5 billion miles from the star.
The newly-discovered huge structure around HR 4796A may have implications for what the yet-unseen planetary system looks like around the 8-million-year-old star, which is in its formative years of planet construction.
“This newly-discovered debris field of very fine dust was likely created from collisions among developing infant planets near HR 4796A, evidenced by the inner ring of dust,” said University of Arizona astronomer Glenn Schneider and co-authors, who used Hubble’s Space Telescope Imaging Spectrograph (STIS) to probe and map the small dust particles in the outer reaches of the HR 4796A system.
“The pressure of starlight from the star then expelled the dust far into space.”
But the dynamics don’t stop there. The puffy outer dust structure is like a donut-shaped inner tube that got hit by a truck. It is much more extended in one direction than in the other and so looks squashed on one side even after accounting for its inclined projection on the sky.
This may be due to the motion of the host star plowing through the interstellar medium, like the bow wave from a boat crossing a lake.
Or it may be influenced by a tidal tug from the star’s red dwarf binary companion, HR 4796B, located at least 54 billion miles from the primary star.
“The dust distribution is a telltale sign of how dynamically interactive the inner system containing the ring is,” Dr. Schneider said.
“We cannot treat exoplanetary debris systems as simply being in isolation. Environmental effects, such as interactions with the interstellar medium and forces due to stellar companions, may have long-term implications for the evolution of such systems.”
“The gross asymmetries of the outer dust field are telling us there are a lot of forces in play (beyond just host-star radiation pressure) that are moving the material around.”
“We’ve seen effects like this in a few other systems, but here’s a case where we see a bunch of things going on at once.”
A report on the discovery is published in the Astronomical Journal.
_____
Glenn Schneider et al. 2018. The HR 4796A Debris System: Discovery of Extensive Exo-ring Dust Material. AJ 155, 77; doi: 10.3847/1538-3881/aaa3f3
