Sci & Tech

‘Double’ Galaxy Mystifies Hubble Astronomers – “We Were Really Stumped”

Hamilton's Object

This Hubble Space Telescope snapshot reveals three magnified photos of a distant galaxy embedded in a cluster of galaxies. These photos are produced by a trick of nature referred to as gravitational lensing. The galaxy cluster’s immense gravity magnifies and distorts the sunshine from the distant galaxy behind it, creating the a number of photos. The galaxy cluster, catalogued as SDSS J223010.47-081017.8, is 7 billion light-years from Earth. Hubble has noticed many gravitationally lensed galaxies. However, the pictures noticed on this Hubble snapshot are distinctive. Two of the magnified photos, proven within the pull-out at backside proper, are precise copies of one another. The two shiny ovals are the cores of the galaxy. This uncommon phenomenon happens as a result of the background galaxy straddles a ripple within the material of house. This “ripple” is an space of best magnification, attributable to the gravity of dense quantities of darkish matter, the unseen glue that makes up many of the universe’s mass. As gentle from the faraway galaxy passes by means of the cluster alongside this ripple, two mirror photos are produced, together with a 3rd picture that may be seen off to the facet. A detailed-up of the third picture is proven within the pull-out at high proper. This picture most intently resembles the distant galaxy, which is situated greater than 11 billion light-years away. Based on a reconstruction of this picture, the researchers decided that the distant galaxy seems to an edge-on, barred spiral with ongoing, clumpy star formation. The mirror photos are named “Hamilton’s Object” for the astronomer who found them. Credit: Joseph DePasquale (STScI)

Gazing into the universe is like wanting right into a funhouse mirror. That’s as a result of gravity warps the material of house, creating optical illusions.

Many of those optical illusions seem when a distant galaxy’s gentle is magnified, stretched, and brightened because it passes by means of a large galaxy or galaxy cluster in entrance of it. This phenomenon, referred to as gravitational lensing, produces a number of, stretched, and brightened photos of the background galaxy.

This phenomenon permits astronomers to review galaxies so distant they can’t be seen apart from by the results of gravitational lensing. The problem is in attempting to reconstruct the distant galaxies from the odd shapes produced by lensing.

But astronomers utilizing the Hubble Space Telescope stumbled upon one such odd form whereas analyzing quasars, the blazing cores of lively galaxies. They noticed two shiny, linear objects that gave the impression to be mirror photos of one another. Another oddball object was close by.

The options so befuddled the astronomers that it took them a number of years to unravel the thriller. With the assistance of two gravitational-lensing consultants, the researchers decided that the three objects have been the distorted photos of a faraway, undiscovered galaxy. But the largest shock was that the linear objects have been precise copies of one another, a uncommon incidence attributable to the exact alignment of the background galaxy and the foreground lensing cluster.

Hubble Space Telescope Over Earth

3D animation displaying the Hubble Space Telescope over the Earth. Credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)

Astronomers have seen some fairly bizarre issues scattered throughout our huge universe, from exploding stars to colliding galaxies. So, you’d assume that once they see an odd celestial object, they’d be capable to determine it.

But NASA’s Hubble Space Telescope uncovered what seems to be a pair of similar objects that look so bizarre it took astronomers a number of years to find out what they’re.

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

The oddball objects encompass a pair of galaxy bulges (the central star-filled hub of a galaxy) and a minimum of three almost parallel cut up streaks. Hamilton noticed them accidentally whereas utilizing Hubble to survey a set of quasars, the blazing cores of lively galaxies.

After chasing dead-end theories, soliciting assist from colleagues, and doing plenty of head-scratching, Hamilton and the rising staff, led by Richard Griffiths of the University of Hawaii in Hilo, lastly put collectively the entire clues to resolve the thriller.

The linear objects have been the stretched photos of a gravitationally lensed distant galaxy, situated greater than 11 billion light-years away. And, they gave the impression to be mirror photos of one another.

The staff found that the immense gravity of an intervening, and uncatalogued, foreground cluster of galaxies was warping house, magnifying, brightening, and stretching the picture of a distant galaxy behind it, a phenomenon referred to as gravitational lensing. Though Hubble surveys reveal a number of these funhouse-mirror distortions attributable to gravitational lensing, this object was uniquely perplexing.

In this case, a exact alignment between a background galaxy and a foreground galaxy cluster produces twin magnified copies of the identical picture of the distant galaxy. This uncommon phenomenon happens as a result of the background galaxy straddles a ripple within the material of house. This “ripple” is an space of best magnification, attributable to the gravity of dense quantities of darkish matter, the unseen glue that makes up many of the universe’s mass. As gentle from the faraway galaxy passes by means of the cluster alongside this ripple, two mirror photos are produced, together with a 3rd picture that may be seen off to the facet.

Griffiths compares this impact to the brilliant wavy patterns seen on the underside of a swimming pool. “Think of the rippled surface of a swimming pool on a sunny day, showing patterns of bright light on the bottom of the pool,” he defined. “These bright patterns on the bottom are caused by a similar kind of effect as gravitational lensing. The ripples on the surface act as partial lenses and focus sunlight into bright squiggly patterns on the bottom.”

In the gravitationally lensed distant galaxy, the ripple is vastly magnifying and distorting the sunshine from the background galaxy that’s passing by means of the cluster. The ripple acts like an imperfect curvy mirror that generates the twin copies.

Solving the Mystery

But this uncommon phenomenon wasn’t well-known when Hamilton noticed the unusual linear options in 2013.

As he regarded by means of the quasar photos, the snapshot of the mirrored photos and parallel streaks stood out. Hamilton had by no means seen something prefer it earlier than, and neither had different staff members.

“My first thought was that maybe they were interacting galaxies with tidally stretched-out arms,” Hamilton mentioned. “It didn’t really fit well, but I didn’t know what else to think.”

So Hamilton and the staff started their quest to resolve the thriller of those tantalizing straight strains, later dubbed Hamilton’s Object for its discoverer. They confirmed the unusual picture to colleagues at astronomy conferences, which elicited quite a lot of responses, from cosmic strings to planetary nebulae.

But then Griffiths, who was not a member of the unique staff, supplied probably the most believable clarification when Hamilton confirmed him the picture at a NASA assembly in 2015. It was a magnified and distorted picture attributable to a lensing phenomenon much like these seen in Hubble photos of different large galaxy clusters which can be amplifying photos of very distant galaxies. Griffiths confirmed this concept when he realized of an identical linear object in one among Hubble’s deep-cluster surveys.

The researchers, nevertheless, nonetheless had an issue. They couldn’t determine the lensing cluster. Normally, astronomers who examine galaxy clusters first see the foreground cluster that’s inflicting the lensing, after which discover the magnified photos of distant galaxies inside the cluster. A search of the Sloan Digital Sky Survey photos revealed {that a} galaxy cluster resided in the identical space because the magnified photos, but it surely didn’t present up in any catalogued survey. Nevertheless, the truth that the unusual photos have been on the heart of a cluster made it clear to Griffiths that the cluster was producing the lensed photos.

The researchers’ subsequent step was in figuring out whether or not the three lensed photos have been on the similar distance, and subsequently have been all of the distorted portraits of the identical faraway galaxy. Spectroscopic measurements with the Gemini and W. M. Keck observatories in Hawaii helped the researchers make that affirmation, displaying that the lensed photos have been from a galaxy situated greater than 11 billion light-years away.

The distant galaxy, based mostly on a reconstruction of the third lensed picture, seems to be an edge-on, barred spiral with ongoing, clumpy star formation.

Around the identical time because the spectroscopic observations by Griffiths and undergraduates in Hilo, a separate group of researchers in Chicago recognized the cluster and measured its distance utilizing Sloan knowledge. The cluster resides greater than 7 billion light-years away.

But, with little or no details about the cluster, Griffiths’ staff was nonetheless fighting easy methods to interpret these uncommon lensing shapes. “This gravitational lens is very different from most of the lenses that were studied before by Hubble, particularly in the Hubble Frontier Fields survey of clusters,” Griffiths defined. “You don’t have to stare at those clusters for long to find many lenses. In this object, this is the only lens we have. And we didn’t even know about the cluster at first.”

Mapping the Invisible

That’s when Griffiths referred to as an skilled on gravitational lensing concept, Jenny Wagner of the University of Heidelberg in Germany. Wagner had studied comparable objects and, with colleague Nicolas Tessore, now on the University of Manchester in England, developed laptop software program for deciphering distinctive lenses like this one. Their software program helped the staff work out how all three lensed photos got here to be. They concluded that the darkish matter across the stretched photos needed to be “smoothly” distributed in house at small scales.

“It’s great that we only need two mirror images in order to get the scale of how clumpy or not dark matter can be at these positions,” Wagner mentioned. “Here, we don’t use any lens models. We just take the observables of the multiple images and the fact they can be transformed into one another. They can be folded into one another by our method. This already gives us an idea of how smooth the dark matter needs to be at these two positions.”

This result’s necessary, Griffiths mentioned, as a result of astronomers nonetheless don’t know what darkish matter is, almost a century after its discovery. “We know it’s some form of matter, but we have no idea what the constituent particle is. So we don’t know how it behaves at all. We just know that it has mass and is subject to gravity. The significance of the limits of size on the clumping or smoothness is that it gives us some clues as to what the particle might be. The smaller the dark matter clumps, the more massive the particles must be.”

The staff’s paper seems within the September difficulty of The Monthly Notices of the Royal Astronomical Society.

Reference: “Hamilton’s Object – a clumpy galaxy straddling the gravitational caustic of a galaxy cluster: constraints on dark matter clumping” by Richard E Griffiths, Mitchell Rudisel, Jenny Wagner, Timothy Hamilton, Po-Chieh Huang and Carolin Villforth, 17 May 2021, The Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stab1375

The Hubble Space Telescope is a mission of worldwide cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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