NASA / ESA / IAA
The Hubble Space Telescope's closeup view of the "Jewel Box" star cluster NGC
4755 reveals sapphire blue supergiant stars, one ruby-red supergiant and other
stellar gems. Click on the picture for larger views from the European Hubble team.
An antique "Jewel Box" in the night sky takes on a new shine in imagery from three of the best telescopes in the world and in space.
The Jewel Box is a well-known star cluster in the constellation Crux, the "Southern Cross." To the naked eye, the cluster looks like a single star that is listed in the catalogs as Kappa Crucis. But when seen through a telescope, the Jewel Box reveals gems of reddish and bluish stars. Its name was inspired back in the 1830s by English astronomer John Herschel, who compared the grouping to "a casket of variously colored precious stones."
In scientific terms, the cluster also known as NGC 4755 is about 6,400 light-years from Earth. The 100 or so stars in the cluster all condensed from a single huge cloud of gas and dust about 16 million years ago. But the stars were formed in a wide variety of sizes, ranging from supergiants that are 20 times heavier than our sun to dwarfs that are less than half the sun's mass.
That size difference explains why the stars' colors are different as well. The bigger a star is, the more brightly it shines and the faster it ages. And that's what makes the Jewel Box so interesting to astronomers. In one place, they can compare how big and little stars have evolved over the same time period.
The closest-in of the new views comes from the Hubble Space Telescope's Wide Field Camera 2, not long before a shuttle crew replaced the camera with a brand-new instrument.
"This new Hubble image of the core of the cluster represents the first comprehensive far ultraviolet to near-infrared image of an open galactic cluster," the European Space Agency's Hubble team says in today's advisory. "It was created from images taken through seven filters, allowing viewers to see details never seen before."
ESO / NASA / ESA / DSS2 / IAA
This series of images zooms in progressively on the Jewel Box star cluster, starting
with a 35mm camera shot (top left), then the Digitized Sky Survey 2 view (middle
left), then the view from the Wide Field Imager on the MPG/ESO 2.2-meter
telescope (upper right), then FORS1 on the ESO's Very Large Telescope (lower left),
and finally the Hubble view. Click on the image for a bigger picture.
The view from the FORS1 instrument on the European Southern Observatory's Very Large Telescope in Chile takes a step back for a wider view of the whole cluster. The ESO says this image of the Jewel Box is "one of the best ever taken from the ground."
The MPG/ESO 2.2-meter telescope's Wide Field Imager took an even bigger step back, producing a picture that puts the star cluster in cosmic perspective. In this view, you can see that the Jewel Box is surrounded by a sparkling sea of stars.