Midsummer's Dream Galaxies

What does the galaxy in which we live look like?
It is almost certain that we will never be able to send a probe out of our Milky Way to take a snapshot, in the same way as the first satellites could do to give us striking images of planet Earth. But astronomers do not need this to imagine what our bigger home resembles. And they have a pretty good idea of it.

The Milky Way with its several hundreds of billion stars is thought to be a relatively flat disc - 100,000 light-year across [1] - with a central bulge lying in the direction of the constellation Sagittarius (The Archer) and six spiral arms. The Milky Way has most probably also a central bar made of young, bright stars.

If we can't take pictures of the Milky Way, we may photograph others galaxies which astronomers think look similar to it. The two galaxies presented here are just two magnificient examples of barred spiral galaxies. One - Messier 83 - is seen face-on, and the other - NGC 4565 - appears edge-on. Together, they give us a nice idea of how the Milky Way may appear from outer space.

These images are based on data obtained with the twin FORS1 and FORS2 (FOcal Reducer and Spectrograph) instruments attached to two ESO's 8.2-m Unit Telescopes of the Very Large Telescope Array located on Cerro Paranal. The data were extracted from the ESO Science Archive Facility, which contains approximately 50 Terabytes [2] of scientific data and is, since April 1, 2005, open to the worldwide community. These invaluable data have already led to the publication of more than 1000 scientific papers. They also contains many nice examples of beautiful astronomical objects which could be the theme of as many midsummer's dreams.

NGC 4565
The first galaxy pictured here is NGC 4565 [3], which for obvious reasons is also called the Needle Galaxy. First spotted in 1785 by Uranus' discoverer, Sir William Herschel (1738-1822), this is one of the most famous example of an edge-on spiral galaxy and is located some 30 million light-years away in the constellation Coma Berenices (Berenice's Hair). It displays a bright yellowish central bulge that juts out above most impressive dust lanes.

Because it is relatively close (it is only 12 times farther away than Messier 31, the Andromeda galaxy, which is the major galaxy closest to us) and relatively large (roughly one third larger than the Milky Way), it does not fit entirely into the field of view of the FORS instrument (about 7 x 7 arcmin2).

Many background galaxies are also visible in this FORS image, giving full meaning to their nickname of "island universes".

Messier 83
If our Milky Way were to resemble this one, we certainly would be proud of our home! The beautiful spiral galaxy Messier 83 [4] is located in the southern constellation Hydra (the Water Snake) and is also known as NGC 5236 and as the Southern Pinwheel galaxy. Its distance is about 15 million light-years. Being about twice as small as the Milky Way, its size on the sky is 11x10 arcmin2.

The image show clumpy, well-defined spiral arms that are rich in young stars, while the disc reveals a complex system of intricate dust lanes. This galaxy is known to be a site of vigorous star formation.


[1]: A light-year is the distance that light travels in a vacuum in a year - about 9.46 million million kilometres.

[2]: 1 Terabyte = 1012 byte = 1000 Gigabyte = 1 million million byte.

[3]: "NGC" means "New General Catalogue" (of nebulae and clusters) that was published in 1888 by J.L.E. Dreyer in the "Memoirs of the Royal Astronomical Society".

[4]: French astronomer and comet hunter Charles Messier (1730-1817) is the author of world famous "Catalog of Nebulae and Star Clusters" containing more than 100 objects.

Source: ESA

Related stories:

When It Comes to Galaxies, Diversity Is Everywhere
(PhysOrg.com) -- There's an old saying in astronomy: "Galaxies are like people. They're only normal until you get to know them." That view is supported by a group of astronomers after using NASA's Hubble Space Telescope to study a large number of galaxies in our cosmic backyard.
Scientists find black hole 'missing link'
Scientists at Durham University have found the "missing link" between small and super-massive black holes.
Immigrant Sun: Our star could be far from where it started in Milky Way
A long-standing scientific belief holds that stars tend to hang out in the same general part of a galaxy where they originally formed. Some astrophysicists have recently questioned whether that is true, and now new simulations show that, at least in galaxies similar to our own Milky Way, stars such as the sun can migrate great distances.
1843 stellar eruption may be new type of star explosion
Eta Carinae, the galaxy's biggest, brightest and perhaps most studied star after the sun, has been keeping a secret: Its giant outbursts appear to be driven by an entirely new type of stellar explosion that is fainter than a typical supernova and does not destroy the star.
The thousand-ruby galaxy
ESO's Wide Field Imager has captured the intricate swirls of the spiral galaxy Messier 83, a smaller look-alike of our own Milky Way. Shining with the light of billions of stars and the ruby red glow of hydrogen gas, it is a beautiful example of a barred spiral galaxy, whose shape has led to it being nicknamed the Southern Pinwheel.
Scientists discover minimum mass for galaxies
(PhysOrg.com) -- By analyzing light from small, faint galaxies that orbit the Milky Way, UC Irvine scientists believe they have discovered the minimum mass for galaxies in the universe – 10 million times the mass of the sun.
XMM-Newton's massive discovery
(PhysOrg.com) -- ESA's orbiting X-ray observatory XMM-Newton has discovered the most massive cluster of galaxies seen in the distant Universe until now. The galaxy cluster is so big that there can only be a handful of them at that distance, making this a rare catch indeed. The discovery confirms the existence of dark energy.
Most Black Holes Might Come in Only Small and Large
(PhysOrg.com) -- Black holes are sometimes huge cosmic beasts, billions of times the mass of our sun, and sometimes petite with just a few times the sun's mass. But do black holes also come in size medium? A new study suggests that, for the most part, the answer is no.

News discussion:

Space & Earth science news