Disturbing the Universe

David L Clements, science and science fiction


Pythagoras’ Trousers and Herschel

Several of us were interviewed by Chris North at a recent Herschel meeting about what we thought were the highlights of the mission. This was broadcast on Radio Cardiff on 19th May as part of the Pythagoras’ Trousers programme. I don’t know where they got that title but at least they know how to use apostrophes.

You can now hear this section of the programme here.

At the end of the segment, starting at about 17 minutes in, is an attempt to explain the Herschel mission in ordinary plain language, using a script by Jon Brumfitt & Leo Metcalfe read by me. I’m glad that’s all clear now.

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Press Release: Four new galaxy clusters take researchers further back in time

I have a press release out today! Below is the text from the release from Imperial. So far it seems to have been picked up by:

The Daily Mail

The Financial Express

The Economic Times


scientias.nl (in Dutch)

and there may be more to come.

Not sure what to think about the Daily Mail entry – it’s not my favourite paper, but, as a colleague said, ‘if your piece is next to “Lauren Goodger shows off the results of her new boob job in unflattering sheer dress at charity event” and “What happened to natural beauty, Kim? Kardashian overdoes her look with thick, heavy make-up arriving at Khloe’s house” you’re certainly reaching new audiences.’

News: science

Imperial College London

Four new galaxy clusters take researchers further back in time

by Gail Wilson12 February 2014

main image


Four unknown galaxy clusters each potentially containing thousands of individual galaxies have been discovered some 10 billion light years from Earth.

An international team of astronomers, led by Imperial College London, used a new way of combining data from the two European Space Agency satellites, Planck and Herschel, to identify more distant galaxy clusters than has previously been possible. The researchers believe up to 2000 further clusters could be identified using this technique, helping to build a more detailed timeline of how clusters are formed.

– Dr Dave Clements

Study author

Galaxy clusters are the most massive objects in the universe, containing hundreds to thousands of galaxies, bound together by gravity. While astronomers have identified many nearby clusters, they need to go further back in time to understand how these structures are formed. This means finding clusters at greater distances from the Earth.

The light from the most distant of the four new clusters identified by the team has taken over 10 billion years to reach us. This means the researchers are seeing what the cluster looked like when the universe was just three billion years old.

Lead researcher Dr David Clements, from the Department of Physics at Imperial College London, explains: “Although we’re able to see individual galaxies that go further back in time, up to now, the most distant clusters found by astronomers date back to when the universe was 4.5 billion years old. This equates to around nine billion light years away. Our new approach has already found a cluster in existence much earlier than that, and we believe it has the potential to go even further.”

The clusters can be identified at such distances because they contain galaxies in which huge amounts of dust and gas are being formed into stars. This process emits light that can be picked up by the satellite surveys.

Galaxies are divided into two types: elliptical galaxies that have many stars, but little dust and gas; and spiral galaxies like our own, the Milky Way, which contain lots of dust and gas. Most clusters in the universe today are dominated by giant elliptical galaxies in which the dust and gas has already been formed into stars.

“What we believe we are seeing in these distant clusters are giant elliptical galaxies in the process of being formed,” says Dr Clements.

Observations were recorded by the Spectral and Photometric Imaging Receiver (SPIRE) instrument as part of Herschel Multi-tiered Extragalactic Survey (HerMES). Seb Oliver, Head of the HerMES survey said: “The fantastic thing about Herschel-SPIRE is that we are able to scan very large areas of the sky with sufficient sensitivity and image sharpness that we can find these rare and exotic things.  This result from Dr. Clements is exactly the kind of thing we were hoping to find with the HerMES survey”

The researchers are among the first to combine data from two satellites that ended their operations last year: the Planck satellite, which scanned the whole sky, and the Herschel satellite, which surveyed certain sections in greater detail. The researchers used Planck data to find sources of far-infrared emission in areas covered by the Herschel satellite, then cross referenced with Herschel data to look at these sources more closely. Of sixteen sources identified by the researchers, most were confirmed as single, nearby galaxies that were already known. However, four were shown by Herschel to be formed of multiple, fainter sources, indicating previously unknown galaxy clusters.

The team then used additional existing data and new observations to estimate the distance of these clusters from Earth and to determine which of the galaxies within them were forming stars. The researchers are now looking to identify more galaxy clusters using this technique, with the aim of looking further back in time to the earliest stage of cluster formation.

The research involved scientists from the UK, Spain, USA, Canada, Italy and South Africa. It is published in the Monthly Notices of the Royal Astronomical Society.

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Herschel: The End of the End

SPIRE, the UK-led instrument on the Herschel Space Observatory, which was the first instrument turned on during the on orbit commissioning back in May 2009, has now been turned off. It was the last instrument on Herschel to be switched off after the technical tests following the end of helium, and thus the end of observations, earlier this year.

Herschel is over.

Long live Herschel!

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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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Submillimetre Astronomy: Fun Times!

While we all wait for the Planck results to be announced on 21st March (just one week to go until you all learn The Answer!), other branches of astronomy have been making some progress  as well.

My own particular brand, far-IR and submm extragalactic astronomy, has had a few good days. Yesterday the ALMA telescope (Atacama Large Millimetre Array) was inaugurated. This is a stupendously powerful new instrument that can do in minutes observations that were not even possible before from the ground. It is, arguably, more powerful in many ways than the Hubble Space Telescope, especially when you consider that most of the things it observers are not bright in the optical and near-IR and thus can’t be observed properly by Hubble in the first place.

A good example of this is the second bit of good news in my department. Colleague Joaquin Vieira has made observations of a whole bunch of candidate high redshift, gravitationally lensed submm galaxies with ALMA and found lots of interesting sources, confirming that they are indeed at high redshift. To some extent we already knew this thanks to observations with the Herschel Space Observatory, but Joaquin’s ALMA images are truly stunning in their quality, especially since they were observed in only a few minutes and with the array only 1/4 finished.

You can read the paper itself, soon to be out in Nature, here, but watch this space, since we will have our own news in this same department very soon!