Disturbing the Universe

David L Clements, science and science fiction

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Merger Reveals Secrets of Galaxy Formation: Another Press Release

We had another paper out in Nature this week, a further product of Herschel and the HerMES survey.

This is what ESA had to say about our results:


A rare encounter between two gas-rich galaxies spotted by ESA’s Herschel space observatory indicates a solution to an outstanding problem: how did massive, passive galaxies form in the early Universe?

Most large galaxies fall into one of two major categories: spirals like our own Milky Way that are full of gas and actively forming stars, or gas-poor ellipticals, populated by old cool red stars and showing few signs of ongoing star formation.

It was long assumed that the large elliptical galaxies seen in the Universe today built up gradually over time via the gravitational acquisition of many small dwarf galaxies. The theory held that the gas in those galaxies would gradually be converted into cool, low-mass stars, so that by today they would have exhausted all of their star-forming material, leaving them ‘red and dead’.

So the discovery in the last decade that very massive elliptical galaxies had managed to form during just the first 3–4 billion years of the Universe’s history posed something of a conundrum. Somehow, on short cosmological timescales, these galaxies had rapidly assembled vast quantities of stars and then ‘switched off’.

One idea is that two spiral galaxies might collide and merge to produce a vast elliptical galaxy, with the collision triggering such a massive burst of star formation that it would rapidly deplete the gas reservoir. In a new study using Herschel data, astronomers have captured the onset of this process between two massive galaxies, seen when the Universe was just 3 billion years old.

The galaxy pair was initially identified in the Herschel data as a single bright source, named HXMM01. Follow-up observations showed that it is in fact two galaxies, each boasting a stellar mass equal to about 100 billion Suns and an equivalent amount of gas.

The galaxies are linked by bridge of gas, indicating that they are merging.

“This monster system of interacting galaxies is the most efficient star-forming factory ever found in the Universe at a time when it was only 3 billion years old,” says Hai Fu from University of California, Irvine, USA, who led the study published in Nature.

“The HXMM01 system is unusual not only because of its high mass and intense star-forming activity, but also because it exposes a crucial, intermediate step of the merging process, providing valuable insight that will help us constrain models for the formation and evolution of galaxies,” adds co-author Asantha Cooray, also from University of California, Irvine.

The onset of the merger has sparked a star-formation frenzy, with the system spawning stars at a phenomenal rate equivalent to roughly 2000 stars like the Sun every year. By comparison, a galaxy like the Milky Way today only manages to produce the equivalent of one Sun-like star per year.

Furthermore, the efficiency with which gas is being converted into stars is around ten times higher than that seen in more normal galaxies, which form stars at much slower rates.

Such a high star-formation rate is not sustainable, however, and the gas reservoir contained in the HXMM01 system will be quickly exhausted, quenching further star formation and leading to an aging population of low-mass, cool, red stars.

Dr Fu’s team estimate that it will take about 200 million years to convert all the gas into stars, with the merging process completed within a billion years. The final product will be a massive red and dead elliptical galaxy of about 400 billion solar masses.

“We were very lucky to catch this extreme system in such a critical transitional phase. It shows that the merger of gas-rich and actively star-forming galaxies is a possible mechanism to form the most massive ellipticals that are observed in the young Universe,” says Seb Oliver from University of Sussex, UK, and Principal Investigator for the HerMES Key Programme, within which the data have been collected.

“This discovery highlights the importance of the vast sky-scanning surveys that were completed with Herschel. In this case, the exceptional source HXMM01 was revealed, which may point to a solution of the riddle of how very massive galaxies formed and evolved when the Universe was still young,” adds Göran Pilbratt, ESA’s Herschel Project Scientist.

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Press Release: Star Factory in Distant Universe Challenges Galaxy Evolution Models

We have a Press Release out!

Sadly, the news from Waco, Texas bumped us off the Today programme this morning, but we may be back tomorrow. In the interim you can read about our new results, out in Nature today, below and at other places like ESA and Universe Today.

Imperial College Press Release:

Astronomers have discovered an extremely distant galaxy that is expanding by more than 2000 new stars each year.

Using the European Space Agency’s Herschel space observatory they have seen images of the galaxy as it was when the Universe was less than a billion years old.

This is the most active that astronomers have seen such a young galaxy and since this discovery they are re-thinking some fundamental ideas about how galaxies form and evolve over time.

The newly discovered galaxy, known as HFLS3, appears as a faint red smudge in images from the observatory’s Herschel Multi-tiered Extragalactic Survey (HerMES). In reality, this represents the activities of a star-building factory, which is transforming gas and dust into new stars.

“This particular galaxy got our attention because it was bright, and yet very red compared to others like it,” says Herschel researcher Dr Dave Clements from the Department of Physics at Imperial College London.

Tens of thousands of massive, star-forming galaxies have been detected by Herschel as part of HerMES and sifting through them to find the most interesting ones is a challenge.

HFLS3 has one of the highest star formation rates astronomers have seen; over a thousand times faster than our own galaxy, the Milky Way.

According to current theories of galaxy evolution, galaxies as massive as HFLS3 should not be present so soon after the Big Bang.

Even at its young age of 880 million years, HFLS3 was already close to the mass of the Milky Way, with a mass of stars and star-forming material roughly 140 billion times that of our Sun.

The astronomers have calculated that light from HFLS3 has travelled for almost 13 billion years across space, and that by now, it may have grown to be as big as the most massive galaxies known in the local Universe.

The first galaxies were thought to be relatively small and lightweight, containing only a few billion times the mass of our Sun.

They formed their first stars at rates just a few times more than the number the Milky Way does today, then grew by feeding off cold gas from intergalactic space and by merging with other small galaxies.

“With these observations, Herschel has found a rare example of a galaxy bursting with stars at a time in cosmic history when there were very few such galaxies,” says Göran Pilbratt, ESA’s Herschel Project Scientist.

The mere existence of a single such object so early in the Universe poses a challenge to current theories of early galaxy formation, which predict that they should reach such large masses only much later.

The team are continuing to comb the enormous dataset from Herschel looking for more examples of such extreme, early galaxies.

“A DustObscured Massive HyperStarburst Galaxy at Redshift 6.34” by D. A. Riechers et al. is published in Nature, 18 April 2013.

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Upcoming publication (scientific)

We have a paper coming out in Nature on 18th April.

Can’t say what it’s about as the Nature embargo applies as much to blogs as to more traditional media, but it is an interesting paper, though probably not as amusing as the fiction I wrote for Nature Futures a while back.

More news once I can write about it!


Sad News: John Maddox RIP

Nature announced today the death of John Maddox at the weekend. John was the editor of Nature for two long stints and was largely responsible for making it one of the prime scientific journals in the world today. I well remember his editorials when i was a graduate student.

I remember more, though, his time on the BBC Radio 3 programme ;Scientifically Speaking. I don’t know if Radio 3 still has a scientific spot, but in my school days SS was a highlight for me. Unlike Radio 4’s Science Now it covered one subject per programme and it covered it in depth. I still remember Maddox speaking at length about QED as I lay listening to it on my parents’ bed.

John Maddox had a very distinctive voice, one that worked well on radio. I wish he had done more on radio, and maybe television as well, but then we would have lost his role in making Nature what it is today. I suspect I’ll be looking at his book What Remains to be Discoevered at the weekend.