Close-Up of the Sun

The sun. (Image credit: NASA)

The Conversation contributed the article to's expert voices.

The Professor of Astrophysics is Michael Murphy.

Physicists have been trying to explain nature's laws for a long time. Everything from why you don't fall through the floor to why the sky is blue is explained by the law of electromagnetism.

The theory of electromagnetism is the best physical theory humans have ever created, but it has no answer for why it is so strong. The strength of electromagnetism is measured by a number called alpha or the fine-structure constant.

Physicists should "put this number up on their wall and worry about it", according to the American physicist who helped come up with the theory.

There are a lot of stars in the universe.

We decided to study stars that are almost identical to our sun in order to see if is the same in different places. If is different in different places, we might be able to find the ultimate theory, not just of electromagnetism, but of all nature's laws together.

We want to break our favorite theory

Physicists want a situation where our understanding of physics is broken down. There is a new physics. Current theories can't explain a signal. The theory of everything is the subject of a sign post.

They could wait in a gold mine for particles of dark matter to collide with a special crystal. They might care for the world's best atomic clocks for a long time to make sure they tell the right time. There is a ring of the Large Hadron collider that has the speed of light in it's grip.

It's difficult to find where to look. Our current theories don't work.

It is easy to search in laboratories on Earth. The drunk was only looking for his lost keys under a lamp-post when he might have lost them on the other side of the road.

rainbow of brightly colored bars with small black lines through them

The sun's rainbow: sunlight is here spread into separate rows, each covering just a small range of colors, to reveal the many dark absorption lines from atoms in the sun's atmosphere. (Image credit: N.A. Sharp / KPNO / NOIRLab / NSO / NSF / AURA, CC BY)

Stars are terrible, but sometimes terribly similar

We decided to look beyond our solar system to see if stars which are similar to our sun produce the same rainbow of colors. Some of the light is absorbed by the atoms in the atmosphere of stars.

Dark lines in the rainbow are caused by the absorption of certain colors. The absorption colors are determined by the dark lines.

Hotter and cooler gas bubbling through the turbulent atmospheres of stars make it hard to compare absorption lines in stars with those seen in laboratory experiments.

A view of the sun captured by the Daniel K. Inouye Solar Telescope in Hawaii. (Image credit: NSO / AURA / NSF, CC BY)

The atmospheres of stars are moving and this causes the lines to shift. Any chance of measuring is ruined because of the shifts. It seems that stars are not a good place to test electromagnetism.

We wondered if stars that are twins of each other have the same colors. Twins of our sun were compared to each other.

A new test with solar twins

At the University of New South Wales and the Swinburne University of Technology, we measured the spacing between the absorption lines in our sun and the 16 solar twins.

The stars were seen on the 3.6-metre European Southern Observatory telescope. While not the largest telescope in the world, the light it gathers is fed into the best-controlled, best-understood spectrograph. The light is separated into its colors by this.

It takes a lot of time to look for planets. This gave us the data we needed.

The ESO 3.6-metre telescope in Chile spends much of its time observing sun-like stars to search for planets using its extremely precise spectrograph, HARPS.

The ESO 3.6-metre telescope in Chile spends much of its time observing sun-like stars to search for planets using its extremely precise spectrograph, HARPS. (Image credit: Iztok Bončina / ESO, CC BY)

We were able to show that was the same in the 17 solar twins as it was in the 17 suns. You compare your height to the diameter of the Earth. The most precise test of it's kind has ever been done.

Our favorite theory didn't change despite our new measurement. The stars we've studied are relatively close to each other.

What's next?

New solar twins are half way to the center of our universe.

There should be a lot of dark matter in this region. Like, we don't know a lot about dark matter, and some physicists think the inner parts of our universe might be just the dark corner.

We might find the keys to the universe if we can see the suns with the largest telescopes.

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