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Home / Science / & # 39; First Light & # 39; achieved in an experiment that could reveal the secret of dark energy

& # 39; First Light & # 39; achieved in an experiment that could reveal the secret of dark energy



As an astronomer, there is no better feeling than "first light" with a new instrument or telescope. It is the culmination of years of preparation and building of new hardware that for the first time collects light particles from an astronomical object.

This is usually followed by a relieved breath and then the excitement about the new science that is now possible.

On October 22, the Dark Energy Spectroscopic Instrument (DESI) was deployed on the Mayall Telescope in Arizona, USA. reached first light. This is a tremendous step forward in measuring galaxy distances, ushering in a new era of mapping of the structures in the universe.

As the name implies, this may also be the key to solving one of physics biggest questions: What is it? the mysterious power called "dark energy" that makes up 70 percent of the universe?

The cosmos is lumpy. Galaxies live together in groups of a few to ten galaxies. There are also clusters of a few hundred to a thousand galaxies and superclusters containing many such clusters.

This hierarchy of the universe is known from the first maps of the universe, which appeared in the diagrams of what looked like a "stickman" groundbreaking center for astrophysics (CfA) Redshift Survey.

These stunning images were the first glimpses of large-scale structures in the universe, some of which spanned hundreds of millions of light-years.

The CfA survey was painstakingly created one after the other. The spectrum of galaxy light was measured ̵

1; a split of light by wavelength or color – and the fingerprints of certain chemical elements (mainly hydrogen, nitrogen and oxygen) were identified.

These chemical signatures are systematically shifted to longer redness wavelengths due to the expansion of the universe.

 File 20191027 113972 1hmy009 SDSS card – every point is a galaxy. (M. Blanton / SDSS / CC BY-SA)

This "redshift" was first discovered by the astronomer Vesto Slipher and led to the famous Hubble Law – the observation that more distant galaxies exist seem to move faster.

This means that near-by galaxies appear to be relatively slow in removing them – they are less redshifted than distant galaxies. Measuring the redshift of a galaxy is therefore a way to measure its distance.

What matters is that the exact relationship between redshift and distance depends on the expansion history of the universe, which can be calculated theoretically with our theory of gravitation and our assumptions of matter and energy density of the universe.

All these assumptions were finally tested at the turn of the century with the combination of new observations of the universe, including new 3D maps from larger redshift surveys.

In particular, the Sloan Digital Sky Survey (SDSS) was the first special redshift survey telescope to measure more than one million redshifts in galaxies, mapping the large-scale structure in the universe down to the smallest detail.

The SDSS cards contained hundreds of super clusters and filaments, helping to make an unexpected discovery – dark energy. They showed that the matter density of the universe was much smaller than expected from the cosmic microwave background, the light left over from the Big Bang.

This meant that there had to be an unknown substance called dark energy that accelerates the expansion of the universe and the increasing absence of matter.

The Riddle

The combination of all these observations heralded a new era of cosmological understanding with a universe composed of 30 percent matter and 70 percent dark energy.

But despite the fact that most physicists have now assumed that there is something like dark energy, we still do not know the exact shape.

However, there are several possibilities. Many researchers believe that the energy of the vacuum simply has a specific value called the "cosmological constant."

Other options are the possibility that Einstein's highly successful theory of gravitation is incomplete when used on a large scale throughout the universe.

New tools like DESI will support the next step in solving the puzzle. It will measure tens of millions of redshifts of galaxies covering a huge volume of the universe of up to ten billion light-years from Earth.

Such a stunning, detailed map should be able to answer some key questions about the dark energy and evolution of large-scale structures in the universe.

For example, it should tell us if dark energy is just a cosmological constant. This is done by measuring the ratio of the pressure that the dark energy exerts on the universe to the energy per unit volume.

If the dark energy is a cosmological constant, then this ratio should be constant both in the cosmic time and in the cosmic place. For other explanations, however, this ratio would vary. Any indication that it is not a constant would be revolutionary and would trigger intense theoretical work.

DESI should also be able to constrain and even kill many theories of modified gravity, possibly providing a strong affirmation of Einstein's Theory of General Theory.

Or the opposite – and that in turn would trigger a revolution in theoretical physics.

Another important theory tested with DESI is inflation, which predicts tiny random variations in primary-energy density. The universe was exponentially expanded during a brief period of intense growth to become the germs of today's large-scale structures.

DESI is just one of several next-generation dark energy missions and experiments that are set to be optimistic in the next decade that we can soon solve the mystery of dark energy.

New satellite missions like Euclid and massive ground-based observation also provide insights such as the Large Synoptic Survey Telescope.

Other redshifting instruments such as DESI, including 4MOST at the European Southern Observatory. Together, they will cause hundreds of millions of redshifts across the sky, leading to an unimaginable map of our cosmos.

It seems to be a long time ago when I wrote my dissertation based on just 700 redshifts of galaxies. It really shows that being an astronomer is an exciting time.  The Conversation

Bob Nichol, Professor of Astrophysics and Pro-Vice Chancellor (Research and Innovation), University of Portsmouth.

This article was republished from The Conversation under a Creative Commons license. Read the original article.


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