Tag: Dark matter

The Universe May Be Expanding Faster Than We Thought. Does It Mean Something?

At the beginning of time, all the matter in the universe was compressed into an infinitesimally small point. That tiny speck of everything then exploded and formed the universe.

In some sense, it’s still exploding, expanding at an accelerating rate.

In the past, scientists have looked to the radiation left behind from the Big Bang — its smoking gun — to calculate what the rate of the expanding universe ought to be today.

But new evidence, soon to be published in The Astrophysical Journal, suggests these estimates may be wrong, or at least incomplete.

New observations from the Hubble Space Telescope have indicated that the universe may be expanding 5 to 9 percent faster than predicted by the Big Bang.




But how?

Using the Hubble, scientists from across the US were able to painstakingly measure the distance to stars and supernovae in many galaxies.

They then used this data to refine what’s known as the “Hubble constant,” the rate by which the universe expands, as measured by direct observations.

But when this new “Hubble constant” was compared with the estimates from the Big Bang inferences, the numbers just didn’t match.

You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” Adam Riess, the Nobel laureate at the Space Telescope Science Institute and Johns Hopkins University, who led the project, explained Thursday in a statement.

“But now the ends are not quite meeting in the middle and we want to know why.”

Add this to the long list of questions physicists still have about the universe

The prediction based on the Big Bang “should match our measurement,” Lucas Macri, a Texas A&M physicist and one of the study’s co-authors, tells me.

“If they don’t … there must be a physical reason why these two things are not agreeing.”

So what accounts for the discrepancy?

Either there’s something about the Big Bang that previous estimates have not accounted for or there are factors that come into play after the Big Bang that scientist don’t yet understand.

Macri highlights four possible explanations.

The first is related to the Big Bang.

)We’re seeing evidence of a previously unknown subatomic particle that was abundant right after the Big Bang (a.k.a. ‘dark radiation’),” he says.

If you change the assumptions about what was in the primordial soup, things will have shifted a bit.

The other possibilities are related to “dark energy” and “dark matter,” the substances that make up most of the universe yet can’t be directly observed.

2) Dark energy — the mysterious force that opposes gravity and is causing the universe to accelerate — “is growing in strength and ‘pushing’ galaxies apart faster than it did before,” he says.

3) Dark matter — matter that we can’t see but that is theorized to exist and make up most of the matter in the universe — “is even weirder than we thought.

Or it could not so simply be:

4)Our theory of gravity is incomplete.”

He also mentions that their results aren’t set in stone. “There’s one chance in 1,000 that we got this measurement by accident,” he says.

Physics requires a one in 4 million chance for results to be considered truth. More observations will need to be made.

Macri says he and other researchers will know more soon, especially if they get to use the James Webb Space Telescope, which will replace Hubble in the year 2018.

The James Webb will be able to look much deeper into space than Hubble and can refine the Hubble constant estimate further.

A modest amount of time with James Webb will allow us to make a very significant improvement on our measurement,” Macri says.

Overall, he says, it’s important to know the exact rate of universal expansion because it will yield a more accurate age of the universe.

To get the age of the universe you need to have the Hubble constant,” he says. Right now the uncertainty of their estimate is 2.4 percent, which is the best yet. But not good enough.

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Mysterious Dark Matter May Not Always Have Been Dark

The nature of dark matter is currently one of the greatest mysteries in science. The invisible substance — which is detectable via its gravitational influence on “normal” matter — is thought to make up five-sixths of all matter in the universe.

Astronomers began suspecting the existence of dark matter when they noticed the cosmos seemed to possess more mass than stars could account for.

For example, stars circle the center of the Milky Way so fast that they should overcome the gravitational pull of the galaxy’s core and zoom into the intergalactic void.

Most scientists think dark matter provides the gravity that helps hold these stars back.




Scientists have mostly ruled out all known ordinary materials as candidates for dark matter. The consensus so far is that this missing mass is made up of new species of particles that interact only very weakly with ordinary matter.

One potential clue about the nature of dark matte rhas to do with the fact that it’s five times more abundant than normal matter, researchers said.

This may seem a lot, and it is, but if dark and ordinary matter were generated in a completely independent way, then this number is puzzling,” said study co-author Pavlos Vranas, a particle physicist at Lawrence Livermore National Laboratory in Livermore, California.

Instead of five, it could have been a million or a billion. Why five?

The researchers suggest a possible solution to this puzzle: Dark matter particles once interacted often with normal matter, even though they barely do so now.

The protons and neutrons making up atomic nuclei are themselves each made up of a trio of particles known as quarks.

The researchers suggest dark matter is also made of a composite “stealth” particle, which is composed of a quartet of component particles and is difficult to detect.

The scientists’ supercomputer simulations suggest these composite particles may have masses ranging up to more than 200 billion electron-volts, which is about 213 times a proton’s mass.

Quarks each possess fractional electrical charges of positive or negative one-third or two-thirds. In protons, these add up to a positive charge, while in neutrons, the result is a neutral charge.

Quarks are confined within protons and neutrons by the so-called “strong interaction.

The researchers suggest that the component particles making up stealth dark matter particles each have a fractional charge of positive or negative one-half, held together by a “dark form” of the strong interaction.

Stealth dark matter particles themselves would only have a neutral charge, leading them to interact very weakly at best with ordinary matter, light, electric fields and magnetic fields.

The researchers suggest that at the extremely high temperatures seen in the newborn universe, the electrically charged components of stealth dark matter particles could have interacted with ordinary matter.

However, once the universe cooled, a new, powerful and as yet unknown force might have bound these component particles together tightly to form electrically neutral composites.

Stealth dark matter particles should be stable — not decaying over eons, if at all, much like protons.

However, the researchers suggest the components making up stealth dark matter particles can form different unstable composites that decay shortly after their creation.

These unstable particles might have masses of about 100 billion electron-volts or more, and could be created by particle accelerators such as the Large Hadron Collider (LHC) beneath the France-Switzerland border. They could also have an electric charge and be visible to particle detectors, Vranas said.

Experiments at the LHC, or sensors designed to spot rare instances of dark matter colliding with ordinary matter, “may soon find evidence of, or rule out, this new stealth dark matter theory,” Vranas said in a statement.

If stealth dark matter exists, future research can investigate whether there are any effects it might have on the cosmos.

The scientists, the Lattice Strong Dynamics Collaboration, will detail their findings in an upcoming issue of the journal Physical Review Letters.

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Dwarf Galaxies Loom Large in Quest for Dark Matter

In its inaugural year of observations, the Dark Energy Survey has already turned up at least eight objects that look to be new satellite dwarf galaxies of the Milky Way.

These miniature galaxies — the first discovered in a decade — shine with a mere billionth of our galaxy’s brightness and each contain a million times less mass.

Astronomers believe the vast majority of material in dwarf galaxies is dark matter, a mysterious substance composing 80 percent of all matter in the universe.

Dwarf galaxies have therefore emerged as prime targets for gathering potential clues about dark matter’s composition.




Some theories suggest dark matter particles and antiparticles should produce telltale gamma rays when they collide with each other.

Accordingly, scientists used the Fermi Gamma-Ray Space Telescope to study the newfound dwarf galaxy candidates, as well as a group of dwarf galaxies already on the books.

The telescope detected no significant gamma-ray signals from either set of dwarf galaxies, however, leaving scientists still in the hunt for dark matter.

On May 15, 2015, The Kavli Foundation spoke with three astrophysicists about the continuing search for dark matter data in space and how dwarf galaxies can help us understand the evolution of our universe.

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