This is an image of one-half of the Hubble Space Telescope field of view in the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). The field contains approximately 150,000 stars, down to 30th magnitude. The stars in the Galactic disk and bulge have a mixture of colours and masses. The field is so crowded with stars because Hubble was looking across 26,000 light-years of space in the direction of the centre of our Galaxy.

Half of these stars are bright enough for Hubble to monitor for any small, brief and periodic dips in brightness caused by the passage of an extrasolar planet passing in front of the star, an event called a transit. Hubble took approximately 520 pictures of this field, at red and blue wavelengths, 22 to 29 February, 2004. The green circles identify 9 stars that are orbited by planets with periods of a few days. Planets so close to their stars with such short orbital periods are called 'hot Jupiters.'

These are considered 'candidate' extrasolar planets because most of them are too faint to allow for spectroscopic observations that would allow for a precise measure of the planet's mass. The Hubble observations allow for a robust statistical estimate of the possible 'false positives', which suggests that at least 45 percent of the candidates must be genuine planets.

The bottom frame identifies one of two stars in the field where astronomers were able to spectroscopically measure the star's back-and-forth wobble due to the pull of the planet. The planet turns out to be less than 3.8 Jupiter masses.

[bottom left text]
Hubble Space telescope observed and identified the host star to a gravitationally lensed planet first discovered in 2003 by ground-based telescopes.

[left box]
A foreground red star and planet drifts toward the sky position of a much farther sunlike background star.

[middle-boxes]
In 2003, the foreground star-planet system slightly amplifies the light of a background star that momentarily aligns with it. This is called a microlensing event.

[right box]
The light from each star is progressively more offset year after year as the foreground star drifts by.

[bottom right box]
In 2005, Hubble Space Telescope observations distinguished the light from the two stars. This was possible because the foreground star turns out to be a different colour from the background star. By observing the stars though a red and blue filter, astronomers were able to enhance the visibility of the offset. The relative offset is 0.7 milliarcseconds (the angular width of a dime seen 3,000 miles away) from the source star. (This is below Hubble's resolution, but still a measurable effect.) The deduced positions of the two stars in 2005 are shown with red and blue crosshatches.

This new NASA/ESA Hubble Space Telescope image shows a star known as R Sculptoris, a red giant located 1500 light-years from Earth in the constellation of Sculptor. Recent observations have shown that the material surrounding R Sculptoris actually forms a spiral structure — a phenomenon probably caused by a hidden companion star orbiting the star. Systems with multiple stars often lead to unusual or unexpected morphologies, as seen, for example, in the wide range of striking planetary nebulae that Hubble has imaged.

R Sculptoris is an example of an asymptotic giant branch (AGB) star. All stars with initial masses up to about eight times that of the Sun will eventually become red giants in the later stages of their lives. They start to cool down and lose a large amount of their mass in a steady, dense wind that streams outwards from the star. With this constant loss of material, red giants like R Sculptoris provide a good portion of the raw materials — dust and gas — used for the formation of new generations of stars and planets. They also show what is likely to happen to the Sun in a few billion years from now, and help astronomers to understand how the elements we are made up of are distributed throughout the Universe.

R Sculptoris itself is located outside the plane of the Milky Way and is easily visible using a moderately sized amateur telescope. In this part of the sky far from the galactic plane, there are relatively few stars but many faint and distant galaxies can be seen.

The black region at the centre of the image has been artificially masked.