Tag Archives: Sloan Digital Sky Survey

Universe Expansion Dark Energy

Dark energy influence on the Universe like a roller coster ride

Universe Expansion Dark Energy

(c) NASA

Scientists with the  Sloan Digital Sky Survey (SDSS-II) have used a novel technique to peer through the nature of dark energy as far as ten billion years ago and measure the  three-dimensional structure of the distant Universe. Tracing this 3-D map scientists were able to assess the influence of dark energy over time, which might help unravel the mysteries of this repulsive force.

For the past five billion years, the Universe expansion rate has been speeding up, a phenomenon attributed to dark energy by astronomers. In the early phase of the Universe, however, a few billion years after the Big Bang, this mysterious force did not have a dominant role as  gravity actually held sway, decelerating cosmic expansion.

“We know very little about dark energy but one of our ideas is that it is a property of space itself – when you have more space, you have more energy,” explained Dr Matthew Pieri, a BOSS team-member.

“So, dark energy is something that increases with time. As the Universe expands, it gives us more space and therefore more energy, and at some point dark energy takes over from gravity to end the deceleration and drive an acceleration,” the Portsmouth University, UK, researcher said.

The new measurement is based on data from the Baryon Oscillation Spectroscopic Survey (BOSS), one of the four surveys that make up SDSS-III, gathered using a novel technique called  “baryon acoustic oscillations” (BAO).  This technique uses small variations in matter left over from the early Universe as a “standard ruler” to compare the size of the Universe at various points in its history.

In order for this technique to work, scientists had to study very distant objects. However, very distant objects, like ancient, far away galaxies are faint and difficult to survey, so the astronomers decided to look after quasars, one of the most energetic objects in the Universe, to map the spread of hydrogen gas clouds in space.

Before the quasars’ electromagnetic radiation emissions reach Earth, they encounter clouds of hydrogen. Part of the light becomes thus absorbed, and the pattern of absorption betrays how the density of gas varies with distance along the line of sight to the telescope.

Measuring this absorption – a phenomenon known as the Lyman-alpha Forest – yields a detailed picture of the gas between us and the quasar.

“It’s a cool technique, because we’re essentially measuring the shadows cast by gas along a single line billions of light-years long,” says Anze Slosar of Brookhaven National Laboratory.

“The tricky part is combining all those one-dimensional maps into a three-dimensional map. It’s like trying to see a picture that’s been painted on the quills of a porcupine.”

Last year, the team of astronomers used data from 10,000 quasars gathered by the SDSS-III’s Baryon Oscillation Spectroscopic Survey (BOSS) to make the first large-scale map of the structure of the faraway “Lyman-alpha forest” gas. However, the resolution wasn’t high enough to detect the subtle variation of baryon acoustic oscillations. Now in their latest survey, the scientists build a map of 50,000 quasars that shows the distribution of hydrogen gas clouds reaching 11 billion light-years away  – just two billion years after the Big Bang itself.

Universe expansion is like a roller coaster ride

“If we think of the Universe as a roller coaster, then today we are rushing downhill, gaining speed as we go,” says Nicolas Busca of the Laboratoire Astroparticule et Cosmologie of the French Centre National de la Recherche Scientifique (CNRS), one of the lead authors of the study.

“Our new measurement tells us about the time when the Universe was climbing the hill – still being slowed by gravity.”

Equipped with this high detail map of BAOs, the scientists were able to paint a picture of how the Universe evolved through out history. For the first time, we see how dark energy worked at a time before the Universe’s current acceleration started.

The BOSS findings show that the expansion of the Universe slowed down some 11 billion years ago as a tug of war ensued  between the attractive gravitational forces of galaxies. As the Universe continued to expand,  the constant repulsive force of dark energy began to dominate as matter was diluted by the expansion of space. This is consistent with current Universe expansion theories.

“No technique has ever been able to probe this ancient era before,” says BOSS principal investigator David Schlegel of the Lawrence Berkeley National Laboratory.

“Back then, the expansion of the Universe was slowing down; today, it’s speeding up. How dark energy caused the transition from deceleration to acceleration is one of the most challenging questions in cosmology.

More than eighty years since Edwin Hubble and Georges Lemaitre first measured the expansion rate of the nearby Universe, the SDSS-III has made the same measurement of the expansion rate of the Universe 11 billion years ago. Currently, the BOSS project is only completed by a third. In the few years, scientists plan to map the locations of a million-and-a-half galaxies and more than 160,000 quasars. By the time SDSS-III is complete, it will have helped transform the Lyman-alpha forest technique from a risky idea into a standard method by which astronomers explore the nature of the faraway Universe, the authors involved in the study claim .

Findings were published in the journal Astronomy and Astrophysics.

The first images from the world’s most powerful camera [STUNNING PHOTOS]

The Dark Energy Camera (DECam) is the most powerful sky survey instrument yet built, a collaborative international effort which took more than eight hard years worth of planning and design. Recently, the camera, installed on top of a mountain in Chile at the Victor Blanco Telescope at the Cerro Tololo Inter-American Observatory, was tested for the first time and came back with some incredible sights.

So far, two images have been released to the public, both taken just a few days ago on September 12. The first one, from above is the stunning  globular star cluster 47 Tucanae, a mere 17,000 light years away. Below is the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies a whooping 60 million light years from Earth.

The DECam, which is photometric imaging camera, was developed by the Dark Energy Survey (DES) collaboration based at the Fermi National Accelerator Laboratory. The instrument works by measuring the amount of light emitted by cosmic objects, rather than spectral details. Consisting of  62 charge-coupled devices (CCDs), which allow for capturing 570 megapixels images, the camera is capable of imaging galaxies up to 8 billion light years away.

Currently, DECAM’s goal is to measure the expansion history of the universe by collecting images of 4,000 distant supernovae and 300 million distant galaxies within the next five years and plotting the largest 3-D map of the Universe. The current largest 3-D map of the Universe has been released by the third Sloan Digital Sky Survey and its largest component, the Baryon Oscillation Spectroscopic Survey (BOSS).

via Gizmodo

This is a still image from a video fly-through of the SDSS-III galaxies mapped in Data Release 9. (c) SDSS

Largest 3-D map of the universe released by the SDSS [VIDEO]

This is a still image from a video fly-through of the SDSS-III galaxies mapped in Data Release 9. (c) SDSS

This is a still image from a video fly-through of the SDSS-III galaxies mapped in Data Release 9. (c) SDSS

Previously, we shared the largest and, respectively, most detailed 3-D maps of the Universe released by the Sloan Digital Sky Survey. Now the survey has released a new, massive update to the map, again, making it the largest 3-D map of the Universe, which pinpoints the locations and distances of over a million galaxies. Were you to envision this 3-D map as a cube, its side would be four billion light-years in distance – yes, this is massive data!

Time capsules? Well, with data from the SDSS one can take a trip down memory lane billion of years back with ease. And by making this data freely available to the public, the survey hopes that astronomers from all around the world can now contribute with distinct findings of their own. In fact, considering the sheer volume of stellar information available, it should keep them busy enough for quite some time.

Improvements to the previously released version include:

  • More than 800,000 new galaxy, quasar and stellar spectra
  • Improved stellar parameters for SEGUE and SDSS-I/II stars
  • Improved astrometric calibration
  • Several small changes to catalog data from DR7 and DR8

It’s worth considering, though, that the data released thus far has been amounted during a mere two years of study, out of the whole six years of the project. Expect an even refined and detailed version to pop-up regularly. The project is called the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), which will measure the positions of massive galaxies up to six billion light-years away, as well as quasars – giant black holes actively feeding on stars and gas – up to 12 billion light-years from Earth.

“What really makes me proud of this survey is our commitment to creating a legacy for the future,” says Michael Blanton, a New York University physics professor who led the team that produced the map. “Our goal is to create a map of the universe that will be used long after we are done, by future generations of astronomers, physicists, and the general public.”

Though barely mentioned, the survey’s goal is most likely that of estimating how much of the Universe is made of “dark matter” and “dark energy,” the even more mysterious force that drives the accelerating expansion of the universe.

“Dark matter and dark energy are two of the greatest mysteries of our time,” said David Schlegel of Lawrence Berkeley National Laboratory, the principal investigator of BOSS. “We hope that our new map of the universe can help someone solve the mystery.”

“This YouTube video shows the positions of the 900,000 luminous galaxies used in these studies. Each green dot represents one galaxy. The image covers a redshift range from 0.25 to 0.75, reaching to six billion years ago. The rotation of the image provides a view that shows what the distribution would look like from all sides. Click on the movie to start or stop playing the movie.”

To view patches of the map, you need to follow instructions here, which include downloading a software and getting adjusted with the rather intuitive package.

The 2.5m Sloan telescope at Apache Point Observatory. (c) SDSS

Survey reveals how dark energy expanded and shaped the Universe

The 2.5m Sloan telescope at Apache Point Observatory. (c) SDSS

The 2.5m Sloan telescope at Apache Point Observatory. (c) SDSS

Encompassing years worth of work, the  Sloan Digital Sky Survey (SDSS-III) has now precisely measured the distance between over a quarter of a million galaxies. As part of the project, called the Baryon Oscillation Spectroscopic Survey, or BOSS, scientists built a massive map of all the studied galaxies so far, some more than six billion years ago – a period that marks a tipping point in the Universe’s history. Around this time, matter became so spread out that gravity wasn’t enough to slow down the Universe’s attraction, and instead dark energy took over causing the Universe to begin an accelerated expansion process which continues to this day. Dark energy is still a huge mystery even to the most enlightened astrophysicists, however what makes the  Baryon Oscillation Spectroscopic Survey extremely exciting so far is that it confirms the theoretical models proposed.

Scientists claim that dark energy accounts for 73% of all the mass-energy in the universe. That’s a massive proportion, considering that dark energy is still just that thing, expressed in cosmological constants in mathematical models. Understanding dark energy, thus, becomes a key prerequisite to holistically understanding the Universe.

“There’s been a lot of talk about using galaxy maps to find out what’s causing accelerating expansion,” says David Schlegel of the Lawrence Berkeley National Laboratory.

“We’ve been making a map, and now we’re using it – starting to push our knowledge out to the distances when dark energy turned on.

The BOSS project was centered around the fascinating  baryon acoustic oscillations. These sound waves were emitted some 30,000 years after the Big Bang and then continued to oscillated throughout for some 350,000 years, when the Universe cooled down and hampered their propagation. Matter clustered around the center and edges of the wave, basically guiding galaxies to form in those areas.

The Sloan Digital Sky Survey found that these galaxies were found to be almost at the exact location predicted by the model, helping scientists measure how fast the Universe was expanding six billion years ago, to an accuracy of two percent.

Besides providing highly accurate measurements of the distances between galaxies, the BOSS also serves as a great experiment for testing Einstein’s Theory of Relativity.

“Since gravity attracts, galaxies at the edges of galaxy clusters fall in toward the centres of the clusters,” says Beth Reid, a NASA Hubble Fellow at Lawrence Berkeley National Laboratory.

“General Relativity predicts just how fast they should be falling. If our understanding of General Relativity is incomplete, we should be able to tell from the shapes we see in BOSS’s maps near known galaxy clusters.”

The rate at which galaxies fall into clusters, however, is well consistent with Einstein’s predictions, thus providing another sound proof debunking General Relativity naysayers.

“We already knew that the predictions of General Relativity are extremely accurate for distances within the solar system,” says Reid, “and now we can say that they are accurate for distances of 100 million light-years.

We’re looking a billion times further away than Einstein looked when he tested his theory, but it still seems to work.”

The survey is still a long way from being finished, as only a third of it was completed thus far. As scientists map the Universe at an even greater scale and dwell deeper, billions of light years farther, the Universe’s secrets will come closer to becoming unraveled.

The findings were published in the journal Cosmology and Extragalactic Astrophysics.

[via io9]

Illustration of where the new SDSS map data exists in space and time.

Astronomers plot largest 3D map of the Universe

Illustration of where the new SDSS map data exists in space and time.

Illustration of where the new SDSS map data exists in space and time.

Unveiled this past weekend, astronomers from the Sloan Digital Sky Survey have created a 3D map of the Universe using the light from 14,000 quasars, some of the brightest bodies in the universe, to illuminate gas clouds in regions of space some 11 billion light years away. From the study‘s abstract:

These features arise as the light from the quasar is absorbed by the intervening neutral hydrogen. This gives one-dimensional information about the fluctuations in the neutral hydrogen density along the line of sight to the quasar. When spectra of many quasars are combined, it allows one to build a three-dimensional image of the fluctuations in the neutral hydrogen density and thus infer the corresponding fluctuations in the matter density.

Previous attempts at creating a working 3D map of the Universe have been with successful results in the past, but they had only gone as far as plotting galaxies 7 billion light-years away from Earth. This new version goes far beyond anything previously attempted in distance and time, as it charts clouds of hydrogen as far as 11 billion light years.

Image courtesy of Sloan Digital Sky Survey

Image courtesy of Sloan Digital Sky Survey

Of course, it’s not like someone will be able to chart through these maps anytime soon, especially considering we’re having difficulties reaching infinitely closer points compared, like Mars, but these mapped out 3D representations will provide absolute invaluable insights towards the formation of the Universe, and help answer numerous puzzling questions astronomers have long been after, including the nature of dark energy.

“We’re looking for a bump in the data that may tell us how fast universe is expanding,” said cosmologist Anže Slosar of Brookhaven National Laboratory, one of the researchers who presented the map May 1 at the American Physical Society meeting in Anaheim, California. “We don’t have enough data to see the bump yet, but we expect to get there in a few years.”

Data for the map was scanned with the help of the Baryon Oscillation Spectroscopic Survey, or BOSS, which can analyze light from individual quasars. The team analyzed 14,000 of about 160,000 known quasars and by 2014 astronomers hope to have 50,000 or 60,000 quasar slices in their grips; enough data, they hope, to finally elaborate a meaningful hypothesis concerning the formation and fate of the Universe. The researchers also plan to release a proper 3-D representation of the data (instead of the 2-D images shown here) for the public by then.

Slice of the full map showing the density of hydrogen gas in the ancient universe. Blue represents little gas, while red represents dense clouds.

Slice of the full map showing the density of hydrogen gas in the ancient universe. Blue represents little gas, while red represents dense clouds.