RCW 120 is a galactic bubble that harbors a very large surprise. A surprise that's at least eight times the mass of the sun.
Nestled in the shell around this large bubble is an embryonic star that
looks set to turn into one of the brightest stars in our Milky Way galaxy.
The galactic bubble is known as RCW 120. It lies about 4,300 light-years
away and has been formed by a star at its center. The star is not
visible at these infrared wavelengths but pushes on the surrounding dust
and gas with nothing more than the power of its starlight. In the 2.5
million years the star has existed, it has raised the density of matter
in the bubble wall so much that the quantity trapped there can now
collapse to form new stars.
The bright knot to the right of the base of the bubble in the
Herschel Space Observatory image below is an unexpectedly large,
embryonic star, triggered into formation by the power of the central
star. Herschel's
observations have shown that it already contains between eight to 10
times the mass of our sun. The star can only get bigger because it is
surrounded by a cloud containing an additional 2,000 solar masses.
Not all of that material will fall onto the star, because even the
largest stars in the galaxy do not exceed 150 solar masses. But the
question of what stops the matter falling onto the star is a puzzle for
modern astronomers.
According to theory, stars should stop forming at about 8 solar
masses. At that mass, they should become so hot that they shine
powerfully at ultraviolet wavelengths. This light should push the
surrounding matter away, much as the central star did to form this
bubble. But clearly sometimes this mass limit is exceeded otherwise
there would be no giant stars in the galaxy.
Astronomers would like to know how some stars seem to defy physics
and grow so large. Is this newly discovered stellar embryo destined to
grow into a stellar monster? At the moment, nobody knows but further
analysis of this Herschel image could give us invaluable clues.
Image credit: ESA/PACS/SPIRE/HOBYS Consortia
Source: The Daily Galaxy via http://www.nasa.gov/mission_pages/herschel/herschel20100506a.html
No hay comentarios:
Publicar un comentario