Other
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996xmm..pres....2.&link_type=abstract
XMM Press Release INFO 2-1996
Other
Scientific paper
Collisions between galaxies, each containing billions of stars, are the biggest events since the origin of the Universe. They may occur often enough to play a major role in the evolution of galaxies, and they provide a major theme for ISO's research teams. Collisions trigger star formation within dense dust clouds. These are opaque to visible light, so that even the Hubble Space Telescope is blind to the events within them. One target for ISO's Camera was a pair of galaxies known as the Antennae, 60 million light- years away. The name comes from antenna-like streamers of stars torn from the galaxies by a collision. The galaxies look quite similar by visible light. With its unprecedented ability to harvest and analyse infrared rays, ISO distinguishes different kinds of commotion provoked by the encounter.
To ISO's penetrating infrared eye, one of the Antennae galaxies shows a large ring of intense starmaking around the central nucleus. This feature is absent in the other galaxy. Another region of star formation extends along a line marking the overlap of the disks of the two galaxies, where the collision is fiercest. ISO's Camera has also observed merging galaxies 230 million light-years away, known as Arp 220. Here the intense infrared emission is concentrated in such a small region that astronomers suspect a possible interaction with a giant black hole.
At a long infrared wavelength, ISO's Photometer has measured the temperature of the dust in a pair of colliding galaxies, NGC 6090. The result is minus 250 degrees Celsius. Astronomers estimate the rate of starmaking in NGC 6090 at 25 sun-like stars created every year in NGC 6090, compared with two or three a year in the Milky Way.
The nearby Whirlpool Galaxy, M51, was ISO's "first light" target on 28 November, when the telescope was opened to the sky. Since then the Camera team has made much better pictures of M51. The infrared images show regions of star formation along the galaxy's spiral arms and on either side of the nucleus.
Prof. Catherine Cesarsky, from Saclay in France, is Principal Investigator for ISO's Camera. She comments : "What excites me most about ISO is that, with our sensitivity, we can look for starbursts in very young galaxies and trace the history of galaxies right through to the present era. Only by studying other galaxies can we fully understand our own Galaxy, the Milky Way, and how it created the conditions for life ".
The birth of stars ISO also pursues starmaking processes within the Milky Way Galaxy. Penetrating the dusty clouds where stars are born, infrared rays can reveal protostars. These are strongly radiating cocoons of dust that surround new stars created by gravity squeezing the cloud. The spectrometers in ISO detect fingerprints of constituents of the clouds, by their emission or absorption of infrared rays at precisely defined wavelengths.
ISO's Short-Wavelength Spectrometer team tested their instrument on a dusty cloud called GL2591, which envelops a newly forming massive star. The astronomers have identified molecules in the solid state as ices, some of them never seen in space before, including hydrogen cyanide ice. Dr. Thijs de Graauw of Groningen in the Netherlands is Principal Investigator for ISO's Short-Wavelength Spectrometer. " We want to know how the Sun and the Earth came into existence," Dr. de Graauw says.
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