How did the universe evolve from such a smooth beginning? To help understand, computational cosmologists and NASA produced the featured time-lapse animated video depicting a computer simulation of part of the universe.
The 100-million light-year simulation starts about 20 million years after the Big Bang and runs until the present. After a smooth beginning, gravity causes clumps of matter to form into galaxies which immediately begin falling toward each other. Soon, many of them condense into long filaments while others violently merge into a huge and hot cluster of galaxies.
Investigating of potential universe attributes in simulations like this have helped shape the engineering design the James Webb Space Telescope, currently scheduled for launch in late 2018.
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Astronomers have shown for the first time how star formation in “dead” galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts. The results will be published in the 17 April 2015 issue of the journal Science.
A major astrophysical mystery has centred on how massive, quiescent elliptical galaxies, common in the modern Universe, quenched their once furious rates of star formation. Such colossal galaxies, often also called spheroids because of their shape, typically pack in stars ten times as densely in the central regions as in our home galaxy, the Milky Way, and have about ten times its mass.
Astronomers refer to these big galaxies as red and dead as they exhibit an ample abundance of ancient red stars, but lack young blue stars and show no evidence of new star formation. The estimated ages of the red stars suggest that their host galaxies ceased to make new stars about ten billion years ago. This shutdown began right at the peak of star formation in the Universe, when many galaxies were still giving birth to stars at a pace about twenty times faster than nowadays.
“Massive dead spheroids contain about half of all the stars that the Universe has produced during its entire life,” said Sandro Tacchella of ETH Zurich in Switzerland, lead author of the article. “We cannot claim to understand how the Universe evolved and became as we see it today unless we understand how these galaxies come to be.”
Tacchella and colleagues observed a total of 22 galaxies, spanning a range of masses, from an era about three billion years after the Big Bang . The SINFONI instrument on ESO’s Very Large Telescope (VLT) collected light from this sample of galaxies, showing precisely where they were churning out new stars. SINFONI could make these detailed measurements of distant galaxies thanks to its adaptive optics system, which largely cancels out the blurring effects of Earth’s atmosphere.
The researchers also trained the NASA/ESA Hubble Space Telescope on the same set of galaxies, taking advantage of the telescope’s location in space above our planet’s distorting atmosphere. Hubble’s WFC3 camera snapped images in the near-infrared, revealing the spatial distribution of older stars within the actively star-forming galaxies.
“What is amazing is that SINFONI’s adaptive optics system can largely beat down atmospheric effects and gather information on where the new stars are being born, and do so with precisely the same accuracy as Hubble allows for the stellar mass distributions,” commented Marcella Carollo, also of ETH Zurich and co-author of the study.
According to the new data, the most massive galaxies in the sample kept up a steady production of new stars in their peripheries. In their bulging, densely packed centres, however, star formation had already stopped.
A leading theory is that star-making materials are scattered by torrents of energy released by a galaxy’s central supermassive black hole as it sloppily devours matter. Another idea is that fresh gas stops flowing into a galaxy, starving it of fuel for new stars and transforming it into a red and dead spheroid.
“There are many different theoretical suggestions for the physical mechanisms that led to the death of the massive spheroids,” said co-author Natascha Förster Schreiber, at the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany. “Discovering that the quenching of star formation started from the centres and marched its way outwards is a very important step towards understanding how the Universe came to look like it does now.”
 The Universe’s age is about 13.8 billion years, so the galaxies studied by Tacchella and colleagues are generally seen as they were more than 10 billion years ago.
This research was presented in a paper entitled “Evidence for mature bulges and an inside-out quenching phase 3 billion years after the Big Bang” by S. Tacchella et al., to appear in the journal Science on 17 April 2015.
The team is composed of Sandro Tacchella (ETH Zurich, Switzerland), Marcella Carollo (ETH Zurich), Alvio Renzini (Italian National Institute of Astrophysics, Padua, Italy), Natascha Förster Schreiber (Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany), Philipp Lang (Max-Planck-Institut für Extraterrestrische Physik), Stijn Wuyts (Max-Planck-Institut für Extraterrestrische Physik), Giovanni Cresci (Istituto Nazionale di Astrofisica), Avishai Dekel (The Hebrew University, Israel), Reinhard Genzel (Max-Planck-Institut für extraterrestrische Physik and University of California, Berkeley, California, USA), Simon Lilly (ETH Zurich), Chiara Mancini (Italian National Institute of Astrophysics), Sarah Newman (University of California, Berkeley, California, USA), Masato Onodera (ETH Zurich), Alice Shapley (University of California, Los Angeles, USA), Linda Tacconi (Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany), Joanna Woo (ETH Zurich) and Giovanni Zamorani (Italian National Institute of Astrophysics, Bologna, Italy).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Gravitational waves distort space, altering the regular signals from pulsars received by the CSIRO Parkes Radio Telescope. Credit: Swinburne Astronomy Productions.
Supermassive black holes: every large galaxy’s got one. But here’s a real conundrum: how did they grow so big?
A paper in today’s issue of Science pits the front-running ideas about the growth of supermassive black holes against observational data — a limit on the strength of gravitational waves, obtained with CSIRO’s Parkes radio telescope in eastern Australia.
“This is the first time we’ve been able to use information about gravitational waves to study another aspect of the Universe — the growth of massive black holes,” co-author Dr Ramesh Bhat from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said.
“Black holes are almost impossible to observe directly, but armed with this powerful new tool we’re in for some exciting times in astronomy. One model for how black holes grow has already been discounted, and now we’re going to start looking at the others.”
The study was jointly led by Dr Ryan Shannon, a Postdoctoral Fellow with CSIRO, and Mr Vikram Ravi, a PhD student co-supervised by the University of Melbourne and CSIRO.
Einstein predicted gravitational waves — ripples in space-time, generated by massive bodies changing speed or direction, bodies like pairs of black holes orbiting each other.
When galaxies merge, their central black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.
“When the black holes get close to meeting they emit gravitational waves at just the frequency that we should be able to detect,” Dr Bhat said.
Played out again and again across the Universe, such encounters create a background of gravitational waves, like the noise from a restless crowd.
Astronomers have been searching for gravitational waves with the Parkes radio telescope and a set of 20 small, spinning stars called pulsars.
Pulsars act as extremely precise clocks in space. The arrival time of their pulses on Earth are measured with exquisite precision, to within a tenth of a microsecond.
When the waves roll through an area of space-time, they temporarily swell or shrink the distances between objects in that region, altering the arrival time of the pulses on Earth.
The Parkes Pulsar Timing Array (PPTA), and an earlier collaboration between CSIRO and Swinburne University, together provide nearly 20 years worth of timing data. This isn’t long enough to detect gravitational waves outright, but the team say they’re now in the right ballpark.
“The PPTA results are showing us how low the background rate of gravitational waves is,” said Dr Bhat.
“The strength of the gravitational wave background depends on how often supermassive black holes spiral together and merge, how massive they are, and how far away they are. So if the background is low, that puts a limit on one or more of those factors.”
Armed with the PPTA data, the researchers tested four models of black-hole growth. They effectively ruled out black holes gaining mass only through mergers, but the other three models are still a possibility.
Dr Bhat also said the Curtin University-led Murchison Widefield Array (MWA) radio telescope will be used to support the PPTA project in the future.
“The MWA’s large view of the sky can be exploited to observe many pulsars at once, adding valuable data to the PPTA project as well as collecting interesting information on pulsars and their properties,” Dr Bhat said.
“Gravitational-wave Limits from Pulsar Timing Constrain Supermassive Black Hole Evolution” published in Science, 18th October 2013.
This is the film from our micro exhibition ‘Measuring the Universe: from the transit of Venus to the edge of the cosmos’, showing 1 March–2 September 2012 at the Royal Observatory Greenwich. rmg.co.uk/visit/events/measuring-the-universe
You can follow our astronomers on Twitter: twitter.com/ROGastronomers
Design and direction:
Kwok Fung Lam
Music and sound effects:
Narration and science advisor:
Dr Olivia Johnson
An international team of astronomers, led by David Sobral from Leinden University of the Netherlands used three telescopes located across the globe to study the trends in star formation, from the earliest stars that made up the first galaxies in the universe, up until now. Their findings suggests something quite shocking .. almost 95% of stars that will ever live have already been born! Before you get too worked up.. let me explain their findings and how they came to them.
Over the course of the last several years, several separate studies have taken place where scientists looked at specific time “epochs” of star formation in the universe, but since different methods and equipment were used by various entities, the ability to compare and critique the results from each of the studies has largely proven to be very difficult. As has developing a “complete” model of the stellar evolutionary process as it has progressed over the past 13 billion years.
However, the combined results of these studies has made a few few points very clear. First, they were able to determine how many stars were formed in the past and they were also able to predict how many stars that should exist now as the universe has aged. Second: “Independent assessments of this quantity seemed to indicate that such a heterogeneous mix of measurements greatly overestimated the quantity of stars in the Universe.”
Instead of comparing the data collected from various organizations, the team decided to develop one robust method that would make the process much easier and far more accurate. Using the combined power of various telescopes including the UK Infrared Telescope, the Subaru Telescope and Chile’s Very Large Telescope, they took measurements of hydrogen H-alpha emission lines, which happens to be a pretty reliable method of tracking star-formation activity. Most stars are composed primarily of hydrogen and after all, it is the most abundant element in the universe.
Keep in mind that we can see the universe has evolved by studying some of the most distant stars and galaxies. Light travels at a finite speed across the vacuum of space. If we look at say, our closest cosmic neighbor, the Andromeda galaxy, which is about 2.5 million light-years from Earth — we are looking at the galaxy as it appeared over 2.5 million years ago, which is how long it took the light from the stars in the galaxy to make its way all the way to us. The same can be said for galaxies farther than Andromeda and even stars within our own galaxy. In fact, it takes 8 minutes for the light from the sun to travel from the sun’s surface to your bedroom window each morning. Telescopes are time machines in a sense.
With that said, Maximizing the full capacity of the telescope’s combined power and their filters capable of seeing light at different wavelengths, the team was able to collect the largest sample of deep space images from various times in the universe’s 13 billion year history. What they found.. is that the number of stars being produced has been steadily declining over the past 11 billion years. Furthermore, it is about 30 times lower at this very moment than it was at its peak about 11 billion years ago. They surmised that if they trend steadily continues, no more than 5% additional stars will be produced in the future.
Apparently, they believe their findings reconciles some of the previous findings that also confirms the notion that the universe may be winding down on the number of stars that are being born. Sobral explains, “If we use our consistent measurement of the star formation history of the Universe to predict the number of stars that should exist across cosmic time, then the numbers are a perfect match to what is actually seen. The two measurements can finally be reconciled. Half of the stars that currently exist in the Universe were formed more than 9 billion years ago in less than 2 billion years, while after that, it took the Universe almost 5 times as much time to produce the same quantity.”
Sobral hopes to continue searching for an answer to the question all of us are surely thinking.. WHY is there such a large gap in the number of stars consistently being born compared to the universe as it existed over the past 2 billion years of its lifespan? It’s also only fair to point out that if the conclusion the team came to is truly correct, the last star the universe develops will still be billions of years from now… long after our sun has fused the last of its hydrogen into helium and transitioned to a red-giant to a white-dwarf. Scientists predict that the less massive counterparts to orange-dwarfs like our sun, red-dwarfs — can reasonably be expected to live hundreds of billions (or up to a trillion) years into the future. So stars in the universe will continue to shine in the distant future.
As one last point of contention here in closing. As far as I can tell, these findings are controversial and even I personally have a hard time accepting the conclusion. Most of the galaxies we’ve spotted (including our own) have several starburst regions where new stars are being concocted. Most of those regions are plentiful since galaxies and even satellite galaxies are constantly merging together, sending large quantities of hydrogen in dense clouds together to form massive balls of plasma like the sun. The same will happen to the Milky Way galaxy when Andromeda ultimately collides with us sometime after the demise of our solar system. As long as there are large quantities of gas present in the universe, there will be new stars being formed, but we also must remember that eventually, be it the big rip or the big freeze, the lights in the universe will go off for the last time. It’s the “when” and the “how” that are still being debated.