Astronomers succeed in measuring size of giant galaxy Messier 87

May 21st, 2009 - 4:41 pm ICT by ANI  

Munich, May 21 (ANI): Using ESO’s (European Southern Observatory’s) Very Large Telescope (VLT), astronomers have succeeded in measuring the size of giant galaxy Messier 87 and were surprised to find that its outer parts have been stripped away by still unknown effects.

The galaxy also appears to be on a collision course with another giant galaxy in this very dynamic cluster.

The new observations reveal that Messier 87’s halo of stars has been cut short, with a diameter of about a million light-years, significantly smaller than expected, despite being about three times the extent of the halo surrounding our Milky Way.

Beyond this zone, only few intergalactic stars are seen.

“This is an unexpected result,” said co-author Ortwin Gerhard. “Numerical models predict that the halo around Messier 87 should be several times larger than our observations have revealed. Clearly, something must have cut the halo off early on,” he added.

The team used FLAMES, the super-efficient spectrograph at ESO’s Very Large Telescope at the Paranal Observatory in Chile, to make ultra-precise measurements of a host of planetary nebulae in the outskirts of Messier 87 and in the intergalactic space within the Virgo Cluster of galaxies, to which Messier 87 belongs.

FLAMES can simultaneously take spectra of many sources, spread over an area of the sky about the size of the Moon.

The new result is quite an achievement.

The observed light from a planetary nebula in the Virgo Cluster is as faint as that from a 30-Watt light bulb at a distance of about 6 million kilometers (about 15 times the Earth-Moon distance).

Furthermore, planetary nebulae are thinly spread through the cluster, so even FLAMES’s wide field of view could only capture a few tens of nebulae at a time.

“It is a little bit like looking for a needle in a haystack, but in the dark”, said team member Magda Arnaboldi. “The FLAMES spectrograph on the VLT was the best instrument for the job,” he added. (ANI)

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