Click on the image for higher resolution (5.0 MB)
This image from the Hubble Space Telescope reveals an ancient, glimmering ball of stars called NGC 1466. It is a globular cluster – a gathering of stars all held together by gravity – that is slowly moving through space on the outskirts of the Large Magellanic Cloud, one of our closest galactic neighbours.
Star clusters are aggregates of many (up to one million) stars. They are active systems in which the mutual gravitational interactions among the stars change their structure over time (known to astronomers as "dynamical evolution"). Because of such interactions, heavy stars tend to progressively sink towards the central region of a star cluster, while low-mass stars can escape from the system. This causes a progressive contraction of the cluster core over different timescales and means that star clusters with the same chronological age can vary greatly in appearance and shape because of their different "dynamical ages". All star clusters, including those in the LMC, have been found to host a special type of re-invigorated stars called blue stragglers. Under certain circumstances, stars receive extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a neighbour, or if they collide.
As a result of dynamical aging, heavier stars sink towards the center of a cluster as the cluster ages, in a process similar to sedimentation, called "central segregation". Blue stragglers are bright, making them relatively easy to observe, and they have high masses, which means that they are affected by central segregation and can be used to estimate the dynamical age of a star cluster.
NGC 1466 certainly is one for extremes. It has a mass equivalent to roughly 140,000 Suns and an age of around 13.1 billion years, making it almost as old as the Universe itself. This fossil-like relic from the early Universe lies some 160,000 light-years away from us. NGC 1466 is one of the 5 clusters in the LMC in which the level of dynamical evolution (or "dynamical age") was measured.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure
0 comment(s):
Post a Comment