Black hole (artist's impression): Artist's impression of a stellar-mass black hole.

Name: Black Hole
Type: Milky Way : Star : Evolutionary Stage : Black Hole
Category: Stars
Release date: 18 November 2002, 15:00
Credit: European Space Agency, NASA and Felix Mirabel (the French Atomic Energy Commission & the Institute for Astronomy and Space Physics/Conicet of Argentina)

The Boomerang Nebula - the coolest place in the Universe?: The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far. The NASA/ESA Hubble Space Telescope image is yet another example of how Hubble's sharp eye reveals surprising details in celestial objects. This NASA/ESA Hubble Space Telescope image shows a young planetary nebula known (rather curiously) as the Boomerang Nebula. It is in the constellation of Centaurus, 5000 light-years from Earth. Planetary nebulae form around a bright, central star when it expels gas in the last stages of its life. The Boomerang Nebula is one of the Universe's peculiar places. In 1995, using the 15-metre Swedish ESO Submillimetre Telescope in Chile, astronomers  Sahai and Nyman revealed that it is the coldest place in the Universe found so far. With a temperature of -272C, it is only 1 degree warmer than absolute zero (the lowest limit for all temperatures). Even the -270C background glow from the Big Bang is warmer than this nebula. It is the only object found so far that has a temperature lower than the background radiation. Keith Taylor and Mike Scarrott called it the Boomerang Nebula in 1980 after observing it with a large ground-based telescope in Australia. Unable to see the detail that only Hubble can reveal, the astronomers saw merely a slight asymmetry in the nebula's lobes suggesting a curved shape like a boomerang. The high-resolution Hubble images indicate that 'the Bow tie Nebula' would perhaps have been a better name. The Hubble telescope took this image in 1998. It shows faint arcs and ghostly filaments embedded within the diffuse gas of the nebula's smooth 'bow tie' lobes. The diffuse bow-tie shape of this nebula makes it quite different from other observed planetary nebulae, which normally have lobes that look more like 'bubbles' blown in the gas. However, the Boomerang Nebula is so young that it may not have had time to develop these structures. Why planetary nebulae have so many different shapes is still a mystery. The general bow-tie shape of the Boomerang appears to have been created by a very fierce 500 000 kilometre-per-hour wind blowing ultracold gas away from the dying central star. The star has been losing as much as one-thousandth of a solar mass of material per year for 1500 years. This is 10-100 times more than in other similar objects. The rapid expansion of the nebula has enabled it to become the coldest known region in the Universe. The image was exposed for 1000 seconds through a green-yellow filter. The light in the image comes from starlight from the central star reflected by dust particles.

Name: Boomerang Nebula, IRAS 12419-5414
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Centaurus
Distance: 5000 light years
Release date: 20 February 2003, 15:00
Credit: European Space Agency, NASA

Blaze of stars in an old galaxy's core: The central region of the small galaxy NGC 1705 blazes with the light of thousands of young and old stars. Astronomers call NGC 1705 a dwarf irregular, that is, a small galaxy lacking regular structure. Knowing how dwarf irregular galaxies evolve tells us a lot about galaxy formation and evolution. At 17 million light-years away, the individual stars of the galaxy NGC 1705 are out of range of all but the sharp eyes of the NASA/ESA Hubble Space Telescope. NGC 1705 is an ideal laboratory to conduct investigations on the history of star formation. Young, blue, hot stars are strongly concentrated toward the galaxy's centre. Older, red, cooler stars are more spread out. This galaxy has been forming new stars throughout its lifetime, but a burst of star-formation activity occurred as recently as 26 to 31 million years ago. This 'starburst' is responsible for many of the young stars on the outskirts of this galaxy's core as well as the central giant star cluster. Many astronomers now believe that dwarf galaxies were the first galaxies to collapse and start forming stars in the early Universe. They represent the building blocks from which more massive objects (spiral and elliptical galaxies) later formed. Nearby small galaxies are thought to be the leftovers of the galaxy-formation process. Dwarf irregular galaxies are probably fairly old stellar systems whose chemical and physical properties may be the result of the process of slow evolution. The Hubble observations of the stars in NGC 1705 and other close irregulars show that these galaxies are several thousand million years old. NGC 1705 could be as old as 13.5 thousand million years. Dwarf irregulars are similar in many ways to very young galaxies, but they are much nearer and easier to study. These galaxies seem to have consumed only a tiny part of their reservoir of gas. Their stars have a much lower fraction of heavy elements than does the Sun. Astronomers therefore think that only a few generations of stars have formed there over time. NGC 1705's age, its irregular shape, and proximity all make it an excellent source of knowledge about galaxy formation and evolution. This image was taken in March 1999 and November 2000 by an international science team led by Monica Tosi at Italy's National Institute of Astrophysics (INAF) at the Osservatorio Astronomico di Bologna. Other team members include Alessandra Aloisi (JHU), Mark Clampin (STScI), Laura Greggio (INAF, Osservatorio Astronomico di Padova), Claus Leitherer and Antonella Nota (STScI). Hubble's Wide Field Planetary Camera 2 observed the galaxy in ultraviolet, blue, visible, and infrared light. Although not included in this image, NICMOS (Near Infrared Camera and Multi Object Spectrometer) observations were also made of the galaxy's central core.

Name: IRAS 04531-5326, NGC 1705
Type: Local Universe : Galaxy : Type : IrregularLocal Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Pictor
Distance: 17 million light years
Release date: 6 March 2003, 15:00
Credit: NASA, ESA and the Hubble Heritage Team STScI/AURA )

Location of star HD 209458 (ground-based image): The parent star of HD 209458b is called HD 209458. It is similar to our Sun and lies 150 light-years from Earth. It is visible with binoculars as a seventh magnitude star in the constellation of Pegasus. This is a 1.9 degree three colour composite from the Digitized Sky Survey. The blue plate (B) is shown in blue, the red plate (R) in green and the infrared plate (I) in red.

Name: HD 209458
Type: Milky Way : Star : Circumstellar Material : Planetary System
Category: Exoplanets
Constellation: Pegasus
Distance: 150 light years
Release date: 12 March 2003, 15:00
Credit: European Space Agency, NASA and the Digitized Sky Survey

Hubble watches light echo from mysterious erupting star (May 2002 image): This is the first in a sequence of four pictures from the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys that dramatically demonstrates the echoing of light through space caused by an unusal stellar outburst in January 2002. The image was taken on 20 May 2002. The image is combined from exposures taken through blue (B), green (V), and infrared (I) filters.

Name: IRAS 07015-0346, V838 Mon
Type: Milky Way : Star : Evolutionary Stage : Red SupergiantMilky Way : Star : Type : Variable
Category: Stars
Constellation: Monoceros
Distance: 20000 light years
Release date: 26 March 2003, 15:00
Credit: NASA, European Space Agency, and H.E. Bond (STScI )