From galaxy collisions to star birth: Missing link found

Mar 29, 2005
From galaxy collisions to star birth: Missing link found

Data from ISO, the infrared observatory of the European Space Agency (ESA), have provided the first direct evidence that shock waves generated by galaxy collisions excite the gas from which new stars will form. The result also provides important clues on how the birth of the first stars was triggered and speeded up in the early Universe.
By observing our galaxy and others, scientists have long concluded that the explosion of massive stars like supernovae generates shock waves and ‘winds’ that travel through and excite the surrounding gas clouds. This process triggers the collapse of nearby gas that eventually leads to the birth of new stars, like a domino effect.

Image: This picture shows the colliding galaxies known as Antennae (NGC4038/4039) located 60 million light years away in the constellation Corvus. Data from ESA's Infrared Space Observatory (ISO) have provided the first direct evidence that shock waves genarated by the collision excite the gas and create the right conditions for star formation. The excited gas is observed in the overlapping region (enclosed within the white dashed lines). New stars will be born there and in the course of the next million year they will make the Antennae galaxies twice as bright in the infrared. Credits: HST image, ESA/NASA

The signature of this process is the radiation emitted by molecular hydrogen. When hydrogen molecules are ‘excited’ by the energy of a nearby explosion, they emit a distinctive type of radiation that can be detected in the infrared.

This type of radiation is also observed in places where galaxies have collided with one another and the formation of new stars goes at a very high rate. So far, however, there was no clear picture of what happens in the time between the collision of two galaxies and the birth of the first new stars.

The missing link has now been found by a team of German astronomers that have analysed ISO data of the galaxy pair nicknamed the ‘Antennae’ (NGC 4038/4039). These two galaxies, located 60 million light-years away in the constellation ‘Corvus’ (the Crow), are currently at an early stage of encounter. The scientists noticed that the overlapping region of the two colliding galaxies is very rich in molecular hydrogen, which is in an excited state.

In particular, the radiation from molecular hydrogen is evenly strong in the northern and southern areas of the overlap region. Much to the team’s surprise, however, there are too few supernova explosions or regions of intense star formation there to explain the observed molecular hydrogen emission. So, the excitation of the molecular hydrogen must be the signature of that observationally rare pre-star birth phase in which hydrogen is excited by the mechanical energy produced in the collision and transported by shock waves. In other words, these results provide the first direct evidence of the missing link between gas collision and the birth of the first stars. The team estimates that when the gas will collapse to form new stars, during the next million years, the Antennae galaxy will become at least two times brighter in the infrared.

The astronomers believe that star formation induced by shocks may have played a role in the evolution of proto-galaxies in the first thousand million years of life of our Universe. Shock waves produced through the collision of proto-galaxies may have triggered the condensation process and speeded-up the birth of the very first stars. These objects, made up of only hydrogen and helium, would otherwise have taken much longer to form, since light elements such as hydrogen and helium take a long time to cool down and condense into a proto-star. Shock waves from the first cloud collisions may have been the helping hand.

These results, to be published this Spring in the scientific journal Astronomy & Astrophysics, were obtained by Martin Haas and Rolf Chini from the AIRUB Institute in Bochum (Germany), and by Ulrich Klaas, from the Max-Planck-Institut für Astronomie in Heidelberg (Germany).

The ESA Infrared Space Observatory (ISO) was launched in 1995 and operated from November that year to May 1998. At that time, it was the most sensitive infrared satellite ever launched and made particularly important studies of the dusty regions of the Universe, where visible light telescopes can see nothing. Regions of intense star formation in the colliding galaxies Antennae, were first discovered by ISO’s ISOCAM instrument in 1996. The wealth of data collected by ISO still produce important science results today, with over 130 publications published every year in the refereed literature.

Source: ESA

Explore further: Spacewalking astronauts finish extensive, trick cable job

add to favorites email to friend print save as pdf

Related Stories

Galactic dinosaurs not extinct

Feb 27, 2015

One of the biggest mysteries in galaxy evolution is the fate of the compact massive galaxies that roamed the early Universe.

Astrophysicist explores star formation in Orion's belt

Feb 26, 2015

U.S. Naval Research Laboratory (NRL) astrophysicist Dr. T.L. Wilson is part of a multi-national research team that has discovered an outburst in the infrared from a deeply embedded protostar. The Herschel ...

What makes the solar system interesting to astronomers?

Feb 17, 2015

While most of us are stuck on planet Earth, we're lucky enough to have a fairly transparent atmosphere. This allows us to look up at the sky and observe changes. The ancients noticed planets wandering across ...

A close call of 0.8 light years

Feb 17, 2015

A group of astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system's distant cloud of ...

Recommended for you

Spacewalking astronauts finish extensive, trick cable job

6 hours ago

(AP)—Spacewalking astronauts successfully completed a three-day cable job outside the International Space Station on Sunday, routing several-hundred feet of power and data lines for new crew capsules commissioned ...

Could the Milky Way become a quasar?

Feb 27, 2015

A quasar is what you get when a supermassive black hole is actively feeding on material at the core of a galaxy. The region around the black hole gets really hot and blasts out radiation that we can see billions ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.