Where did today’s spiral galaxies come from?

Hubble shows that the beautiful spirals galaxies of the modern Universe were the ugly ducklings of six billion years ago.

If confirmed, the finding highlights the importance to many galaxies of collisions and mergers in the recent past. It also provides clues for the unique status of our own galaxy, the Milky Way. Using data from the NASA/ESA Hubble Space Telescope, astronomers have created a census of galaxy types and shapes from a time before Earth and the Sun existed, up to the present day. The results show that, contrary to contemporary thought, more than half of the present-day spiral galaxies had peculiar shapes as recently as 6 billion years ago.


The study of the shapes and formation of galaxies, known as morphology, is a critical and much-debated topic in astronomy. An important tool for this is the ‘Hubble sequence’ or the ‘Hubble tuning-fork diagram’, a classification scheme invented in 1926 by the same Edwin Hubble in whose honour the space telescope is named.

Hubble’s scheme divides regular galaxies into three broad classes — ellipticals, lenticulars and spirals — based on their visual appearance. A fourth class contains galaxies with an irregular appearance.

A team of European astronomers led by François Hammer of the Observatoire de Paris has, for the first time, completed a census of galaxy types at two different points in the Universe’s history — in effect, creating two Hubble sequences — that help explain how galaxies form. In this survey, researchers sampled 116 local galaxies and 148 distant galaxies.

The astronomers show that the Hubble sequence six billion years ago was very different from the one that astronomers see today. “Six billion years ago, there were many more peculiar galaxies than now – a very surprising result,” says Rodney Delgado-Serrano, lead author of the related paper recently published in Astronomy & Astrophysics. “This means that in the last six billion years, these peculiar galaxies must have become normal spirals, giving us a more dramatic picture of the recent Universe than we had before.” The astronomers think that these peculiar galaxies did indeed become spirals through collisions and merging. Although it was commonly believed that galaxy mergers decreased significantly eight billion years ago, the new result implies that mergers were still occurring frequently after that time — up to as recently as four billion years ago. “Our aim was to find a scenario that would connect the current picture of the Universe with the morphologies of distant, older galaxies — to find the right fit for this puzzling view of galaxy evolution,” says Hammer.

Also contrary to the widely held opinion that galaxy mergers result in the formation of elliptical galaxies, Hammer and his team support a scenario in which these cosmic clashes result in spiral galaxies. In a parallel paper published in Astronomy & Astrophysics, they delve further into their ‘spiral rebuilding’ hypothesis, which proposes that peculiar galaxies affected by gas-rich mergers are slowly reborn as giant spirals with discs and central bulges. Although our own Galaxy is a spiral galaxy, it seems to have been spared much of the drama; its formation history has been rather quiet and it has avoided violent collisions in astronomically recent times. However, the large Andromeda Galaxy from our neighbourhood has not been so lucky and fits well into the ‘spiral rebuilding’ scenario. Researchers continue to seek explanations for this.

Notes for editors:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Hammer and his team used data from the Sloan Digital Sky Survey undertaken by Apache Point Observatory, New Mexico, USA, and from the GOODS field and Hubble Ultra Deep Field taken by the Advanced Camera for Surveys aboard Hubble.

R. Delgado-Serrano, et al., 2010, How was the Hubble Sequence 6 Giga-years ago? Astronomy & Astrophysics, 509, A78.

F. Hammer et al., 2009, The Hubble Sequence: just a vestige of merger events? Astronomy & Astrophysics, 507, 1313.

Source: ESA

Close Up Pictures Of Pluto's Face

Since discovered in 1930, there has never been observed which can provide a detailed picture of the face of Pluto. Although Pluto is an interesting object, even a topic of debate will be the definition of Pluto in 2006; but Pluto is still difficult to observe and record the details, because a small and distant.

However, Hubble Space Telescope (HST), has changed all that. With the observations that have been conducted since 1994, until the recent images taken between the years 2002-2003, then obtained a more detailed picture of Pluto, rather than observations that have been made ever. These results are a long way from the details, because the challenge to record details such as a soccer ball from a distance of 60 km.

Change the face of Pluto Hubble Space Telescope is seen. Credit: Hubble

Although the image of the HST is not enough to be able to record details of craters and mountains, and even then if there is one, but the recording is done the world HST indicates that vary in color, from white, dark orange-brown to dark. The colors are believed due to ultra-violet radiation from the sun which is in the distance, breaking the existing methane on Pluto's surface, causing a dark brown residue rich in carbon.

Pluto is also changing illumination, in the northern polar region of southern luminous and dark and reddish. The summer approaching Pluto's north pole causes ice to melt and experiencing freezing in the darker areas due terbayangi on the planet. HST has shown that Pluto is not just a ball of ice and rock, but a world that has a dramatic change in atmosphere.

Change season due to the elliptical orbit of Pluto 248 years along with the slanted axis. Season becomes elliptical symmetry because Pluto's orbit. Spring transition into summer in the polar hemisphere rapidly occurred in the north, because Pluto is moving very fast along the orbit as it moves around the Sun in the direction of approach.

Earth Observation landing between 1988 and 2002 showed the mass multiplication of the atmosphere have all the time allegedly due to heating and sublimation of nitrogen ice. HST images of the season to give an understanding of what happened on Pluto and the fate of the atmosphere.

HST image of this is that terdetil at the moment, at least until the New Horizon spacecraft will fly past Pluto and will record more detailed images again, and give a better picture of what is happening on the surface of Pluto, and was still waiting until 2015 to will come.

Source: Hubblesite and Langit Selatan