Dark matter sheds light on stellar mysteries

All but a tiny portion of the cosmos is an utter mystery — even to astrophysicists.

“We can’t see 95 percent of the universe; we don’t really know what it is,” said Michael Troxel, a post-doctoral fellow at Ohio State’s Center of Cosmology and AstroParticle Physics. “This is about learning more than that it exists.”

Earlier this month, a team of about 400 international astrophysicists released a map of the universe that helps to explain the development of the universe over billions of years.

First-year results from the Dark Energy Survey (DES) confirm that 26 percent of the present state of the universe is made up of dark matter, which provides clumpy structural scaffolding for the cosmos. Another 70 percent is comprised of dark energy, which mysteriously accelerates the universe’s expansion.

“We don’t know what it is. We have no physical theory for it. It appears to be the dominant component of everything that is, and we’d like to understand why,” Eric Huff, a former Buckeye and staff scientist at NASA’s Jet Propulsion Laboratory.

The survey draws from images taken by a 570 megapixel Dark Energy Camera atop the Cerro Tololo InterAmerican Observatory in Chile, key parts of which were built at Ohio State.

This month’s findings were based on data covering an area of the sky equal to about 6,000 full moons and spanning about 26 million galaxies.

The challenge for scientists was to use those images to observe something they cannot see: dark matter.

In a process called gravitational lensing, the survey group was able to map unobservable dark matter in the foreground by measuring how light from background galaxies bends as it passes by and through dark matter.

The idea is similar to knowing how thick a pane of glass is based on how distorted things seem when you look through it, Huff said, or like knowing the shape of a cake by its icing alone.

DES scientists then compared that new data with cosmic microwave background, which lingers from when the universe was less than 400,000 years old.

In its infancy, the universe was filled with photon radiation whose light persists today. For scientists, that radiation serves as a snapshot or relic of the Big Bang.

“That shows us how the universe was when it was 400,000 years old,” said Klaus Honscheid, a physics professor and leader of Ohio State’s DES group. “That’s the seed of the whole story of the development of the universe.”

Over billions of years, little fluctuations in the cosmic microwave background developed into complex galaxies.

Using theoretical calculations and computer simulations, researchers predicted what the universe should look like based on cosmic background radiation. Observations made with the lensing technique matched those predictions within 7 percent.

That’s like detecting what an adult face and body should look like based on observing the moment of conception.

“This is arguably one of the first measurements that’s been really competitive with other ways of understanding the universe,” said Huff.

This month’s results are based on the DES’s first year. The group’s fifth observation season began in August and will extend through February.

Honscheid said he’s confident that the remaining data analysis will edge researchers closer to understanding the cosmos’ most mysterious constituents.

“This shows us that our understanding of the universe is at a level that we can describe it really well,” he said. “We have now reached a precision of measurement … 10, 12 years in the making.”

And in a year roiled by protests over the state of science and fear of serious cuts to research funding, the DES survey shows why pure research remains indispensable, said John Beacom, an Ohio State physics and astronomy professor and director of the university’s Center of Cosmology and Astro Particle Physics.

Einstein’s theories inform how GPS and cell phones function. Last Monday, predictions based on centuries of astronomical studies drew millions to watch the solar eclipse. And already, the DES algorithms developed to detect faint galaxies in images has already been applied to detect details as tiny as an insect perched on a leaf — from a satellite image.

“It’s impossible to predict what any given breakthrough will do for us,” Beacom said. “If we begin with these facts of how the universe works, then it helps us understand the meaning of how we fit in.” closed for utility improvements. Completion: February 2018

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