Вадим Дудченко
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What makes SGAS 0033+02, an extremely distant galaxy in the constellation of Pisces, interesting is a little unusual — it appears not just once in the Hubble image, but three times.

This Hubble image shows a massive galaxy cluster (bottom left corner) and three images of the gravitationally lensed galaxy SGAS 0033+02. The color image was made from separate exposures taken in the visible and infrared regions of the spectrum with Hubble’s Wide Field Camera 3 (WFC3). Five filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / E. Wuyts.

“The thrice-visible galaxy is a little difficult to spot,” the Hubble astronomers said.

“It appears once as a curved arc just to the upper right of the very bright star, and twice more as small round dots above the star and to the right of the star respectively.”

SGAS 0033+02’s multiple appearances in the same image are not the result of an error, but instead are due to a remarkable phenomenon known as gravitational lensing.

This phenomenon can occur when a huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it but in the same line of sight. The effect is like looking through a giant magnifying glass.

It allows astronomers to study the details of early galaxies too far away to be seen with current technology and telescopes.

The simplest type of gravitational lensing occurs when there is a single concentration of matter at the center, such as the dense core of a galaxy.

More complex gravitational lensing arises in observations of massive clusters of galaxies. While the distribution of matter in a galaxy cluster generally does have a center, it is never circularly symmetric and can be significantly lumpy. Background galaxies are lensed by the cluster and their images often appear as short, thin lensed arcs around the outskirts of the cluster.

“SGAS 0033+02 was discovered by its namesake, the Sloan Giant Arcs Survey (SGAS), which aimed to identify highly magnified galaxies that were gravitationally lensed by foreground galaxy clusters,” the researchers said.

“The lensed galaxy is of special interest because of its highly unusual proximity in the sky to a very bright star.”

“The star is useful, because it can be used to calibrate and correct observations of SGAS 0033+02.”


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