Tag Archives: Early Universe

Stellar Baby Boom

Stellar baby boom

Astronomers observe starburst galaxies in early space with the ALMA telescope – and discover the most distant detection of water published to date

March 13, 2013

The most vigorous bursts of star birth in the cosmos took place at least one billion years earlier than previously thought. These new insights were the result of observations with the Atacama Large Millimetre/submillimetre Array (ALMA), which will be officially opened on March 14, 2013. The findings are published in a set of three papers which also report on the most distant detection of water to date. Axel Weiß from the Max Planck Institute for Radio Astronomy in Bonn is first author of one of the publications.

Montage, combining data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The ALMA images, represented in red, show the distant, background galaxies, being distorted by the gravitational lens effect produced by the galaxies in the foreground, depicted in the Hubble data in blue. The background galaxies appear warped into rings of light known as Einstein rings, which encircle the foreground galaxies. Zoom Image

Montage, combining data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The … [more]
© ALMA (ESO/NRAO/NAOJ), Y. Hezaveh et al.

 

The most intense bursts of star birth are thought to have occurred in the early Universe, in massive, bright galaxies. These starburst galaxies convert vast reservoirs of cosmic gas and dust into new stars at a furious pace — many hundreds of times faster than in stately spiral galaxies like our own galaxy, the Milky Way. By looking far into space, at galaxies so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period in the Universe’s youth.

“The more distant the galaxy, the further back in time one is looking, so by measuring their distances we can piece together a timeline of how vigorously the Universe was making new stars at different stages of its 13.7 billion year history,” said Joaquin Vieira (California Institute of Technology, USA), who led the team and is lead author of the paper in the journal Nature.

The international team of researchers first discovered these distant and enigmatic starburst galaxies with the US National Science Foundation’s 10-metre South Pole Telescope (SPT) and then used ALMA to zoom in on them to explore the stellar baby boom in the young Universe. They were surprised to find that many of these distant dusty star-forming galaxies are even further away than expected. This means that, on average, their bursts of star birth took place 12 billion years ago, when the Universe was just under 2 billion years old — a full billion years earlier than previously thought.

This schematic image represents how light from a distant galaxy is distorted by the gravitational effects of a nearer foreground galaxy, which acts like a lens and makes the distant source appear distorted, but brighter, forming characteristic rings of light, known as Einstein rings. An analysis of the distortion has revealed that some of the distant star-forming galaxies are as bright as 40 trillion Suns, and have been magnified by the gravitational lens by up to 22 times. Zoom Image

This schematic image represents how light from a distant galaxy is distorted by the gravitational effects of a nearer … [more]
© ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

 

Two of these galaxies are the most distant of their kind ever seen — so distant that their light began its journey when the Universe was only one billion years old. What’s more, in one of these record-breakers, water is among the molecules detected, marking the most distant observations of water in the cosmos published to date.

The team used the unrivalled sensitivity of ALMA to capture light from 26 of these galaxies at wavelengths of around three millimetres. Light at characteristic wavelengths is produced by gas molecules in these galaxies, and the wavelengths are stretched by the expansion of the Universe over the billions of years that it takes the light to reach us. By measuring the stretched wavelengths, astronomers can calculate how long the light’s journey has taken, and place each galaxy at the right point in cosmic history.

“ALMA’s sensitivity and wide wavelength range mean we could make our measurements in just a few minutes per galaxy — about one hundred times faster than before,” said Axel Weiss (Max Planck Institute for Radio Astronomy in Bonn, Germany), who led the work to measure the distances to the galaxies. “Previously, a measurement like this would have been a laborious process of combining data from both visible-light and radio telescopes.”

In the majority of cases, the ALMA observations alone could pinpoint the distances, but for a few galaxies the team combined the ALMA data with measurements from other telescopes, including the Atacama Pathfinder Experiment (APEX) and ESO’s Very Large Telescope [1].

A number of ALMA antennae bathed in red light seen against the Chajnantor night sky. In the background there is the southern Milky Way on the left and the Magellanic Clouds at the top. Zoom Image

A number of ALMA antennae bathed in red light seen against the Chajnantor night sky. In the background there is the … [more]
ESO/C. Malin

 

The astronomers were using only a partial array of 16 of ALMA’s full complement of 66 giant antennas, as the observatory was still under construction at an altitude of 5000 metres on the remote Chajnantor Plateau in the Chilean Andes. When complete, ALMA will be even more sensitive, and will be able to detect even fainter galaxies. For now, astronomers targeted the brighter ones. They took advantage of a helping hand from nature, too: using gravitational lensing, an effect predicted by Einstein’s general theory of relativity, where light from a distant galaxy is distorted by the gravitational influence of a nearer foreground galaxy, which acts like a lens and makes the distant source appear brighter.

To understand by precisely how much this gravitational lensing brightened the view of the galaxies, the team made sharper images of them using more ALMA observations at wavelengths of around 0.9 millimetres.

“These beautiful pictures from ALMA show the background galaxies warped into multiple arcs of light known as Einstein rings, which encircle the foreground galaxies,” said Yashar Hezaveh (McGill University, Montreal, Canada), who led the study of the gravitational lensing. “We are using the massive amount of dark matter surrounding galaxies half-way across the Universe as a cosmic telescope to make even more distant galaxies appear bigger and brighter.”

Analysis of the distortion reveals that some of the distant star-forming galaxies are as bright as 40 trillion (40 million million) Suns, and that gravitational lensing has magnified this by up to 22 times.

“Only a few gravitationally lensed galaxies have been found before at these submillimetre wavelengths, but now SPT and ALMA have uncovered dozens of them.” said Carlos De Breuck (ESO), a member of the team. “This kind of science was previously done mostly at visible-light wavelengths with the Hubble Space Telescope, but our results show that ALMA is a very powerful new player in the field.”

“This is a great example of astronomers from around the world collaborating to make an amazing discovery with a state-of-the-art facility,” said team member Daniel Marrone (University of Arizona, USA). “This is just the beginning for ALMA and for the study of these starburst galaxies. Our next step is to study these objects in greater detail and figure out exactly how and why they are forming stars at such prodigious rates.”

HOR / NJ

Physical Constant passes Alcohol Test

Physical Constant passes the Alcohol Test

Fundamental properties of molecules have not changed during the past seven billion years

December 13, 2012

The mass ratio of protons and electrons is deemed to be a universal constant. And rightly so, as the latest radio-astronomy observations of a distant galaxy have shown. Scientists at the VU University of Amsterdam and the Max Planck Institute for Radio Astronomy in Bonn used the 100-metre radio telescope in Effelsberg to measure absorption lines of the methanol molecule at a number of characteristic frequencies. The researchers analysed the spectrum of the simplest of all the alcohols in a very distant galaxy. The result: to a high degree of accuracy molecules and molecular matter have the same properties today as they did seven billion years ago. According to this finding, the mass ratio of protons and electrons in particular has changed by less than one hundred thousandth of a percent in this period.

Schematic image of the methanol molecule. The black sphere represents the central carbon atom, the red one an oxygen atom and the grey spheres represent hydrogen atoms. The yellow arrow represents the internal rotation of the molecule, whose impediment causes a quantum tunnel effect. Zoom Image

Schematic image of the methanol molecule. The black sphere represents the central carbon atom, the red one an oxygen … [more]
© VU University Amsterdam / Paul Jansen

 

Measurements are the only way that physicists can find out about fundamental universal constants such as the proton-to-electron ratio. Although all terrestrial experiments produce the same value for this ratio, it would theoretically be possible for the constant to have a different value in different regions of the universe or at different times in its history. The methanol molecule is a suitable sensor for detecting such deviations.

A number of lines in the radio spectrum of this molecule would exhibit a significant frequency shift if the proton-to-electron mass ratio changed, while other lines would not be affected by this shift. A group at the VU University of Amsterdam only recently found out which property makes methanol such a sensitive sensor: ultimately it is a quantum tunnel effect which occurs if the internal rotation of the molecule is impeded. This effect leads to very high values for the sensitivity coefficients of the corresponding spectral lines, which can all be calculated individually.

“This makes the methanol molecule an ideal test case in order to discover a possible change in the proton-to-electron mass ratio over time,” says Wim Ubachs, Professor at the VU University of Amsterdam and head of the physics department. “We therefore proposed a search for line radiation from methanol in the distant universe in order to compare the structure of the molecules thus found with the structure of today’s methanol in laboratory experiments.”

The team observed a galaxy where a number of different molecules had already been observed. The galaxy, which is in the line of sight of a high-intensity radio source called PKS1830-211, is about seven billion light years away from Earth. The scientists aimed for four different line transitions in the radio spectrum of the methanol molecule with their search program. And they were actually able to see all four lines with the aid of the 100-metre radio telescope in Effelsberg.

“As an optical astronomer it has been an interesting experience to carry out observations at the large wavelengths which occur in the radio range,” says Julija Bagdonaite, doctoral student at the VU University of Amsterdam and lead author of the publication. “The methanol molecule had absorbed these radio waves seven billion years ago, and the waves have carried along its fingerprint from the distant past on their passage to Earth.”

By analysing the quantum structure of the methanol molecule the researchers were able to deduce that two of its spectral lines which they observed at frequencies around 25 GHz were influenced hardly at all by a change in the proton-to-electron mass ratio. The other two lines reacted much more sensitively to a modification of this parameter.

“The source we investigated is by far the most suitable of all our observational objects for investigating the validity of our local physics even in very distant exotic environments,” says Christian Henkel from the Max Planck Institute for Radio Astronomy. “It would be fantastic if we could find more sources of this type which we could use to look even further back into the past.”

Aerial view of the radio observatory in Effelsberg with its 100-metre radio telescope. The researchers used this telescope to carry out spectroscopic observations of the methanol molecule in the direction of the far distant galaxy PKS1830-211. Zoom Image

Aerial view of the radio observatory in Effelsberg with its 100-metre radio telescope. The researchers used this … [more]
© MPIfR/Photo: Peter Sondermann/VisCom

 

The scientists also included systematic effects of the observations in the evaluation of the data and thus obtained the following result: in the course of the past seven billion years the mass ratio of protons and electrons has changed by a factor of 10-7 at most and is therefore rightly deemed to be a universal constant. This result can definitely be interpreted to mean that the structure of the molecular matter as derived from spectral observations agrees very accurately with the structure seven billion years ago. Possible deviations amount to a mere one hundred thousandth of a percent or even less.

“If we were really to find deviations in this fundamental constant, we would have a problem with our understanding of the foundations of physics,” concludes Karl Menten, Director at the Max Planck Institute for Radio Astronomy. “Most importantly, this would violate Einstein’s equivalence principle, the cornerstone of the general theory of relativity.”

NJ/ME/HOR