Wed. May 18th, 2022

October 7, 2021

(Nanowerk News) Astronomers have seen some pretty weird things scattered across our vast universe, from exploding stars to colliding galaxies. So you would think that when they see a strange object in the sky, they would be able to identify it.

But NASA’s Hubble Space Telescope revealed what appear to be a pair of identical objects that look so strange that it took astronomers several years to determine what they are.

“We were really blunt,” said astronomer Timothy Hamilton of Shawnee State University in Portsmouth, Ohio.

The Oddball objects consist of a pair of galaxy bulges (the central star-filled hub of a galaxy) and at least three nearly parallel split stripes. Hamilton discovered them by accident while using Hubble to study a collection of quasars, the burning nuclei of active galaxies.

After chasing blindfold theories, asking for help from colleagues and doing lots of head scrapes, Hamilton and the growing team, led by Richard Griffiths of the University of Hawaii at Hilo, finally put together all clues to solve the mystery (The monthly announcements from the Royal Astronomical Society, “Hamilton’s Object – a lumpy galaxy bordering on gravity in a galaxy cluster: limitations of dark matter that clumps”).

The linear objects were the stretched images of a gravity-lined distant galaxy more than 11 billion light-years away. And it seemed to be mirror images of each other. This snapshot of the Hubble Space Telescope shows three magnified images of a distant galaxy embedded in a cluster of galaxies This snapshot of the Hubble Space Telescope shows three enlarged images of a distant galaxy embedded in a cluster of galaxies. These images are produced by a trick of nature called gravitational lenses. The enormous gravity of the galaxy cluster magnifies and distorts the light from the distant galaxy behind, creating more images. The galaxy cluster, cataloged as SDSS J223010.47-081017.8, is 7 billion light-years from Earth. Hubble has observed many gravitational lensed galaxies. However, the images spotted in this Hubble snapshot are unique. Two of the enlarged images, shown in the extract at the bottom right, are exact copies of each other. The two bright ovals are the nuclei of the galaxy. This rare phenomenon occurs because the background galaxy extends over a ripple in space. This “ripple” is an area of ​​greatest magnification, caused by gravity in dense amounts of dark matter, the invisible glue that makes up most of the mass of the universe. As light from the distant galaxy passes through the cluster along this ripple, two mirror images are produced along with a third image that can be seen to the side. A close-up of the third image is displayed in the extract at the top right. This image most closely resembles the distant galaxy, which is located more than 11 billion light-years away. Based on a reconstruction of this image, the scientists determined that the distant galaxy looks like an edge-on-barred spiral with continuous, lumpy star formation. The mirror images are called “Hamilton’s object” for the astronomer who discovered them. (Image: NASA, ESA, Richard Griffiths (University of Hawaii) and Jenny Wagner (Heidelberg University) (click on image to enlarge)

The team discovered that the enormous gravity of an intermediate and uncatalogued foreground cluster of galaxies distorted space, enlarged, illuminated, and stretched the image of a distant galaxy behind it, a phenomenon called the gravitational lens. Although Hubble studies reveal many of these funhouse mirror distortions caused by gravitational lenses, this object was uniquely confusing.

In this case, a precise alignment between a background galaxy and a galaxy cluster in the foreground produces two enlarged copies of the same image of the distant galaxy. This rare phenomenon occurs because the background galaxy extends over a ripple in space. This “ripple” is an area of ​​greatest magnification, caused by gravity in dense amounts of dark matter, the invisible glue that makes up most of the mass of the universe. As light from the distant galaxy passes through the cluster along this ripple, two mirror images are produced along with a third image that can be seen to the side.

Griffiths compares this effect to the bright wavy patterns seen at the bottom of a swimming pool. “Think of the rippled surface of a swimming pool on a sunny day that shows patterns of bright light at the bottom of the pool,” he explained. “These bright patterns on the bottom are caused by a similar kind of effect as gravity lenses. Curls on the surface act as partial lenses and focus sunlight into bright, squirming patterns on the bottom.”

In the gravitational lensed distant galaxy, the ripple greatly magnifies the light from the background galaxy passing through the cluster. The ripple acts as an imperfectly curved mirror that generates duplicate copies.

Solving the mystery

But this rare phenomenon was not known when Hamilton discovered the strange linear features in 2013.

As he looked through the quasar images, the snapshot of mirrored images and parallel streaks emerged. Hamilton had never seen anything like it before, and neither had other team members.

“My first thought was that they might be interacting galaxies with occasionally outstretched arms,” ​​Hamilton said. “It did not fit really well, but I did not know what else to think.”

So Hamilton and the team began their quest to solve the mystery with these teasing straight lines, later called Hamilton’s object for his discoverer. They showed the strange image to colleagues at astronomy conferences, which provoked a series of reactions, from cosmic strings to planetary nebulae.

But then Griffiths, who was not a member of the original team, offered the most likely explanation when Hamilton showed him the image at a NASA meeting in 2015. It was an enlarged and distorted image caused by a lens phenomenon similar to those seen in Hubble images of other massive galaxy clusters that amplify images of very distant galaxies. Griffiths confirmed this idea when he learned about a similar linear object in one of Hubble’s deep cluster studies.

However, the researchers still had a problem. They could not identify the lens cluster. Usually, astronomers studying galaxy clusters first see the foreground cluster causing the lens, and then they find enlarged images of distant galaxies in the cluster. A search of Sloan Digital Sky Survey images revealed that a galaxy cluster resided in the same area as the magnified images, but it did not appear in any cataloged study. Nevertheless, the fact that the strange images were at the center of a cluster made it clear to Griffiths that the cluster was producing the lensed images.

The researchers’ next step was to determine if the three lens images were at the same distance, and therefore all the distorted portraits were of the same distant galaxy. Spectroscopic measurements with the Gemini and WM Keck observatories in Hawaii helped the scientists make that confirmation, showing that the lensed images were from a galaxy located more than 11 billion light-years away.

The distant galaxy, based on a reconstruction of the third lens image, appears to be an edge-on-barred spiral with continuous, lumpy star formation.

Approximately at the same time as the spectroscopic observations of Griffiths and students in Hilo, a separate group of researchers in Chicago identified the cluster and measured its distance using Sloan data. The cluster lives more than 7 billion light-years away.

But with very little information about the cluster, Griffiths’ team was still struggling to interpret these unusual lens shapes. “This gravitational lens is very different from most lenses studied before by Hubble, especially in the Hubble Frontier Fields study of clusters,” Griffiths explained. “You do not have to stare long at those clusters to find many lenses. In this object, this is the only lens we have. And we did not even know about the cluster in the beginning.”

Mapping the invisible

That was when Griffiths called an expert in gravitational lens theory, Jenny Wagner from the University of Heidelberg in Germany. Wagner had researched similar objects and, together with colleague Nicolas Tessore, now at the University of Manchester in England, developed computer software for the interpretation of unique lenses like this. Their software helped the team figure out how all three lens images came to be. They concluded that the dark matter around the stretched images should be “evenly” distributed in space on small scales.

“It’s amazing that we only need two mirror images to get the scale of how lumpy or not dark matter can be in these positions,” Wagner said. “Here we do not use any lens models. We just take observable of the multiple images and the fact that they can be transformed into each other. They can be folded into each other by our method. This already gives us an idea of ​​how smooth the dark matter should be at these two positions. ”

This result is important, Griffiths said, because astronomers still do not know what dark matter is, nearly a century after its discovery. “We know it’s some kind of substance, but we have no idea what that ingredient is. So we do not know at all how it behaves. We just know that it has mass and is subject to gravity. The meaning of boundaries. “The size of the lump or smoothness is that it gives us some clues as to what the particle may be. The smaller the dark matter lumps, the more massive the particles must be.”

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