Youthful-looking galaxy may be an adult: The NASA/ESA Hubble Space Telescope quashed the possibility that what was previously believed to be a toddler galaxy in the nearby universe may actually be considered an adult. Called I Zwicky 18, this galaxy has a youthful appearance that resembles galaxies typically found only in the early universe. Hubble has now found faint, older stars within this galaxy, suggesting that the galaxy may have formed at the same time as most other galaxies. Hubble data also allowed astronomers for the first time to identify Cepheid variable stars in I Zwicky 18, marked by the red circles. These flashing stellar mile-markers were used to determine that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. I Zwicky 18 is classified as a dwarf irregular galaxy and is much smaller than our Milky Way Galaxy. The concentrated bluish-white knots embedded in the heart of the galaxy are two major starburst regions where stars are forming at a furious rate. The wispy blue filaments surrounding the central starburst regions are bubbles of gas that have been blown away by stellar winds and supernovae explosions from a previous generation of hot, young stars. This gas is now heated by intense ultraviolet radiation unleashed by hot, young stars. Besides the bluish-white young stars, white-reddish stars also are visible in both I Zwicky 18 and its companion. These stars may be as old as 10 billion years. The reddish extended objects surrounding I Zwicky 18 and its companion are ancient, fully formed galaxies of different shapes that are much farther away. Hubble data also allowed astronomers for the first time to identify Cepheid variable stars in I Zwicky 18. These flashing stellar mile-markers were used to determine that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. The observations of I Zwicky 18 were taken in 2005 and 2006 with Hubble's Advanced Camera for Surveys. Astronomers made this image by combining observations taken with blue and red filters. The science team consists of Alessandra Aloisi and Marco Sirianni of the European Space Agency and Space Telescope Science Institute; Francesca Annibali, Jennifer Mack, and Roeland van der Marel of the Space Telescope Science Institute; Abhijit Saha of the National Optical Astronomy Observatories; and Gisella Clementini, Rodrigo Contreras, Giuliana Fiorentino, Marcella Marconi, Ilaria Musella, and Monica Tosi of the Italian National Astrophysics Institutes in Bologna and Naples.

Name: I Zw 18
Type: Local Universe : Galaxy : Type : IrregularLocal Universe : Galaxy : Size : Dwarf
Category: Galaxies
Distance: 60 million light years
Release date: 16 October 2007, 16:00
Credit: NASA, ESA, and A. Aloisi (European Space Agency and Space Telescope Science Institute)

I Zwicky 18 (ground-based image): A wide field image of the sky around the galaxy I Zwicky 18 taken on the ground by the Digitized Sky Survey 2. The field of view is approximately 2.7 x 2.8 degrees.

Name: I Zw 18
Type: Local Universe : Galaxy : Type : IrregularLocal Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Ursa Major
Distance: 60 million light years
Release date: 16 October 2007, 16:00
Credit: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

I Zwicky 18 (ground-based image): A wide-field view of the constellation of Ursa Major. The galaxy studied by Hubble astronomers, I Zwicky 18, is located to the right of the asterism seen in this image known as "The Plough" or the "Big Dipper".

Name: Ursa Major
Type: Milky Way : Sky Phenomenon : Night Sky : Constellation
Category: Stars
Release date: 16 October 2007, 16:00
Credit: A. Fujii

Arp 87 from the DSS (ground-based image): An image of the region of sky around Arp 87. The interacting galaxies can just be seen towards the centre of the frame. The field of view is approximately 2.7 by 2.8 degrees across.

Name: Arp 87
Type: Local Universe : Galaxy : Type : Interacting
Category: Galaxies
Constellation: Leo
Distance: 300 million light years
Release date: 30 October 2007, 14:00
Credit: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

Wide-field image of Leo and Arp 87 (ground-based image): A wide-field image showing the constellation of Leo. The interacting galaxy pair, Arp 87, is located to the left of the image above Leos's "hind legs".

Name: Arp 87, Constellation Leo
Type: Milky Way : Sky Phenomenon : Night Sky : ConstellationLocal Universe : Galaxy : Type : Interacting
Category: Galaxies
Distance: 300 million light years
Release date: 30 October 2007, 14:00
Credit: A. Fujii

Comet 17P/Holmes Hubble image series: These images taken by the NASA/ESA Hubble Space Telescope reveal Comet Holmes's bright core. The images show that the coma, the cloud of dust and gas encircling the comet, is getting fainter over time. The coma was brightest in the 29 Oct. image. It is two times fainter on 31 Oct. and nine times dimmer on 4 Nov. than during the 29 Oct. observation. The coma is getting fainter because it is expanding. A huge number of small dust particles were created during the 23 Oct. outburst. Since then those particles have been moving away from the nucleus and filling interplanetary space. The coma therefore is becoming more diffuse over time. The nucleus, however, is still active and is producing a significant amount of new dust. So the region around the nucleus is still much brighter (at least 10 times brighter) than it usually is at this point in the comet's orbit.

Name: 17P/Holmes
Type: Solar System : Interplanetary Body : Comet
Category: Solar System
Release date: 15 November 2007, 15:00
Credit: NASA,ESA, and H. Weaver (The Johns Hopkins University Applied Physics Laboratory)

Ground-based image of Comet 17P/Holmes: This image, taken by an amateur astronomer, shows the location of Comet Holmes on 28 Oct. Superimposed on this image is a graphic showing the comet's path from 30 Sept. to 25 Nov.

Name: 17P/Holmes
Type: Solar System : Interplanetary Body : Comet
Category: Solar System
Release date: 15 November 2007, 15:00
Credit: T. Dickinson, Ontario, Canada