̽��ֱ�� of Cambridge - martin haehnelt

Variations in the ‘fogginess’ of the universe identify a milestone in cosmic history

sc604 — Mon, 15 Apr 2019 23:00:25 +0000

̽��ֱ��results, reported in the Monthly Notices of the Royal Astronomical Society, have enabled astronomers to zero in on the time when reionisation ended and the universe emerged from a cold and dark state to become what it is today: full of hot and ionised hydrogen gas permeating the space between luminous galaxies.

Hydrogen gas dims light from distant galaxies much like streetlights are dimmed by fog on a winter morning. By observing this dimming in the spectra of a special type of bright galaxies, called quasars, astronomers can study conditions in the early universe.

In the last few years, observations of this specific dimming pattern (called the Lyman-alpha Forest) suggested that the fogginess of the universe varies significantly from one part of the universe to another, but the reason behind these variations was unknown.

“We expected the light from quasars to vary from place to place at most by a factor of two at this time, but it is seen to vary by a factor of about 500,” said lead author Girish Kulkarni, who completed the research while a postdoctoral researcher at the ̽��ֱ�� of Cambridge. “Some hypotheses were put forward for why this is so, but none were satisfactory.”

̽��ֱ��new study concludes that these variations result from large regions full of cold hydrogen gas present in the universe when it was just one billion years old, a result which enables researchers to pinpoint when reionisation ended.

During reionisation, when the universe transitioned out of the cosmic ‘dark ages’, the space between galaxies was filled with a plasma of ionised hydrogen with a temperature of about 10,000˚C. This is puzzling because fifty million years after the big bang, the universe was cold and dark. It contained gas with temperatures only a few degrees above absolute zero, and no luminous stars and galaxies. How is it then that today, about 13.6 billion years later, the universe is bathed in light from stars in a variety of galaxies, and the gas is a thousand times hotter?

Answering this question has been an important goal of cosmological research over the last two decades. ̽��ֱ��conclusions of the new study suggest that reionisation occurred 1.1 billion years after the big bang (or 12.7 billion years ago), quite a bit later than previously thought.

̽��ֱ��team of researchers from India, the UK, Canada, Germany, and France drew their conclusions with the help of state-of-the-art computer simulations performed on supercomputers based at the Universities of Cambridge, Durham, and Paris, funded by the UK Science and Technology Facilities Council (STFC) and the Partnership for Advanced Computing in Europe (PRACE).

“When the universe was 1.1 billion years old there were still large pockets of the cosmos where the gas between galaxies was still cold and it is these neutral islands of cold gas that explain the puzzling observations,” said Martin Haehnelt of the ̽��ֱ�� of Cambridge, who led the group that conducted this research, supported by funding from the European Research Council (ERC).

“This finally allows us to pinpoint the end of reionisation much more accurately than before,” said Laura Keating of the Canadian Institute of Theoretical Astrophysics.

̽��ֱ��new study suggests that the universe was reionised by light from young stars in the first galaxies to form.

“Late reionisation is also good news for future experiments that aim to detect the neutral hydrogen from the early universe,” said Kulkarni, who is now based at the Tata Institute of Fundamental Research in India. “ ̽��ֱ��later the reionisation, the easier it will be for these experiments to succeed.”

One such experiment is the ten-nation Square Kilometre Array (SKA) of which Canada, France, India, and the UK are members.

Reference:
Girish Kulkarni et al. ‘Large Ly α opacity fluctuations and low CMB τ in models of late reionisation with large islands of neutral hydrogen extending to z < 5:5.’ Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093/mnrasl/slz025

Large differences in the ‘fogginess’ of the early universe were caused by islands of cold gas left behind when the universe heated up after the big bang, according to an international team of astronomers.

These neutral islands of cold gas explain the puzzling observations

Martin Haehnelt

Amanda Smith, Institute of Astronomy

Artist's impression of reionisation period

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Astronomers find evidence of cosmic climate change

ns480 — Thu, 23 Dec 2010 15:49:48 +0000

̽��ֱ��findings, shortly to be published in the Monthly Notices of the Royal Astronomical Society, were made by researchers measuring the temperature of gas that lies in between galaxies.

They found a clear indication that the temperature of this 'intergalactic medium' had increased steadily between the period when the Universe was one tenth of its current age and the point at which it reached one quarter of its current age.

̽��ֱ��team believe that the effect was caused by objects called quasars; giant accreting black holes at the heart of galaxies - which emit ultraviolet light and triggered a series of reactions in the gas clouds that caused the temperature to rise.

̽��ֱ�� of Cambridge astronomer Dr. George Becker, who led the study, said: "Early in the history of the Universe, the vast majority of matter was not in stars or galaxies. Instead, it was spread out in a very thin gas that filled up all of space."

" ̽��ֱ��gas casts a series of shadows on the light given off by quasars, which are extremely distant, bright objects. By analysing how those shadows block the background light from the quasars, we can infer many of the properties of the absorbing gas, such as where it is, what it's made of, and how hot it is."

̽��ֱ��quasar light the astronomers looked at was more than 10 billion years old by the time it reached Earth and had travelled through vast tracts of the Universe.

As a result, each intergalactic cloud the light passed through during this period left an imprint. ̽��ֱ��cumulative effect can be used as a fossil record of the temperature in the early Universe, just as the Earth's climate might be studied from ice cores and tree rings.

̽��ֱ��temperatures in question were massive compared with standard Earth temperature. ̽��ֱ��research suggests that one billion years after the Big Bang, the gas was a "cool" 8,000 degrees Celsius. By three and half billion years, the temperature had climbed to at least 12,000 degrees.

This warming trend is believed to run counter to normal cosmic climate patterns, as normally the Universe is expected to cool down over time. As the Universe expands, the gas should get colder, much like gas escaping from an aerosol can.

To create the observed rise in temperature, something substantial must have been heating the gas. ̽��ֱ��astronomers believe that the climate change was caused by the huge amount of energy coming from young, active galaxies during this epoch.

Dr. Martin Haehnelt, from the ̽��ֱ�� of Cambridge's Kavli Institute for Cosmology, who also took part in the research, said: " ̽��ֱ��likely culprits are the quasars themselves."

"Over the period of cosmic history we studied, quasars were becoming much more common. These objects, which are thought to be giant black holes swallowing up material in the centres of galaxies, emit huge amounts of energetic ultraviolet light. These UV rays would have interacted with the intergalactic gas, creating the rise in temperature we observed."

One of the lightest and most abundant elements in the intergalactic clouds, Helium, would have played a vital role in the heating process, the researchers suggest.

Ultraviolet light will strip the electrons from a Helium atom, freeing them to collide with other atoms and heat up the gas. Once the supply of fresh helium was exhausted, the Universe would have started to cool down again. Astronomers believe this probably happened when it was about one quarter of its present age. Recent observations with the Hubble Space Telescope also indicate that the interaction between energetic photons and intergalactic Helium had mostly completed by this time.

̽��ֱ��discovery was made possible with data taken with the 10-metre Keck telescopes in Hawaii and was aided by advanced simulations run on a supercomputer at the ̽��ֱ�� of Cambridge. ̽��ֱ��team also included James Bolton ( ̽��ֱ�� of Melbourne) and Wallace Sargent (California Institute of Technology).

Evidence of an intense warming period in the Universe’s early history, described as a form of “cosmic climate change”, has been found by an international team of astronomers.

Early in the history of the Universe, the vast majority of matter was not in stars or galaxies. Instead, it was spread out in a very thin gas that filled up all of space

Dr. George Becker

̽��ֱ�� of Cambridge

cosmic climate change

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Unlocking the secrets of the universe

bjb42 — Tue, 01 Apr 2008 09:00:12 +0000

Astronomers believe that the universe was created 13.7 billion years ago following a cosmic explosion, the residual energy of which can still be detected as cosmic microwave background (CMB) radiation, which fills the universe. ̽��ֱ��matter hurled outwards from the fireball eventually cooled enough to form galaxies across the expanding universe.

Cambridge scientists working with the Institute of Physics of Cantabria in Spain may have discovered a remnant in the CMB from the Big Bang called a ‘texture’. As the universe cooled and underwent transitions, physicists believe that vacuum misalignments or defects occurred. An analogy would be the defects we sometimes see in the transition of water to ice. Textures are one of the most complex of cosmic defects, and when they collapse they form ‘hot’ and ‘cold’ spots in the CMB.

̽��ֱ��team have analysed a large cold spot in the Southern Galactic Hemisphere and published their findings recently in Science. Professor Neil Turok, of the Department of Applied Mathematics and Theoretical Physics (DAMTP), and Dr Mike Hobson, of the Astrophysics Group at the Cavendish Laboratory, concluded that the properties of the cold spot are consistent with its having been formed by a texture. ‘If this is the case,’ said Professor Turok, ‘it will revolutionise our understanding of how the fundamental symmetries between the particles and forces were broken as the universe emerged from the Big Bang.’ Professor Turok was awarded the prestigious Technology, Entertainment, Design (TED) prize in November in recognition of his work in cosmology and his efforts as an education activist. ̽��ֱ��prize is awarded annually to three individuals whose work is considered to have extraordinary potential for positive influence on mankind.

About half a billion years after the Big Bang, it is thought that matter started to aggregate, eventually forming small adolescent proto-galaxies, which then merged to become bigger galaxies. Although astronomers have been able to study starlight of the progenitors of very massive galaxies, starlight from the building blocks of galaxies like our Milky Way has proved elusive. In a recent study, due to be published in March in the Astrophysical Journal, an international team of astronomers led by Dr Martin Haehnelt at the Institute of Astronomy were able to capture starlight from 27 adolescent galaxies about 2 billion years after the Big Bang. They pointed the world’s most powerful telescopes, located in Chile, to the same patch of sky for the equivalent of 12 nights. ‘It is precisely because this was the first time the sky had been searched with this level of sensitivity that we succeeded where many astronomers had failed before,’ said Dr Haehnelt. ̽��ֱ��detection of these building blocks means that scientists can now study in detail how galaxies like the Milky Way have come together.

For more information, please contact Professor Neil Turok(N.G.Turok@damtp.cam.ac.uk), whose research was published in Science (2007) 318, 1612–1614, or Dr Martin Haehnelt (haehnelt@ast.cam.ac.uk).

Cosmic defects and adolescent galaxies – two research projects in Cambridge are bringing us closer to understanding the cosmos.

it will revolutionise our understanding of how the fundamental symmetries between the particles and forces were broken as the universe emerged from the Big Bang.

Professor Neil Turok

Eurritimia from Flickr

big bang

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