Hubble sees a mirror image of the same galaxy thanks to the gravitational lens

Hubble sees a mirror image of the same galaxy thanks to the gravitational lens

It’s been an incredible two weeks for fans of gravitational lenses. JWST made headlines with a spectacular infrared view of the lens in the SMACS 0723 image, and it got everyone talking. Still, seeing gravitationally lensed objects is nothing new. Some can be seen from the ground, and of course the Hubble Space Telescope (HST) has been producing gravitational lensing views for years.

Just a few days ago, HST released another one. This is a striking view of a distant galaxy called SGAS J143845+145407. It is the centerpiece of the HST view and appears twice in a mirror image of itself. The galaxy appears a third time, as a heavily smeared apparition that “bridges” between the other two images.

Deconstruction of the lens of SGAS J143845+145407

So what do we see in the HST image? This triple image object comes from a set of Hubble observations that use gravitational lensing to peer into the interiors of galaxies in the early Universe. It works because the light from these distant galaxies is bent or “bent” by the gravitational influence of a cluster of galaxies that sits between HST and its targets. The cluster is called the “lens” and the distant galaxy, in this case SGAS J143845+145407, is the “lensed object”.

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The gravitational lens can do fun things to the appearance of the lensed object. It can smear the image, distort it and, if the geometry lines up perfectly, create multiple images of it. Finally, the gravitational lens can magnify the view of the aimed object. And that’s important because most of the time these distant objects would be too far away or too faint to observe.

gravitational lens
Gravitational lenses. Source: Cal Tech

The lens reveals details about distant galaxies, such as the existence of spiral arms or star birth regions, which allows astronomers to determine star formation in early galaxies. This gives scientists better insight into how the overall evolution of galaxies has unfolded over time.

About Galaxy SGAS J143845+145407

The triply imaged galaxy in the HST image is technically known as the Luminous Infrared Galaxy (LIRG, for short). A typical LIRG can be as bright as 100 billion times the luminosity of our Sun. Typically, these galaxies are spirals and their infrared luminosity comes from active star-forming regions. Many of them create around 100 new stars a year. For comparison, the Milky Way creates (on average) one new star per year.

A closer view shows more detail in twin images of the lensed galaxy. The third image is the same galaxy spread out between the other two images. Courtesy: NASA/ESA/STScI

Thanks to star formation (and possibly the presence of active galactic nuclei), LIRGs are brighter in infrared light than in optical light. This is because their visible light is absorbed by the gas and dust of the galaxies. The dust then emits thermal energy, which is best seen in the infrared spectrum. Two of HST’s instruments, the Advanced Camera for Surveys and the Wide Field Camera 3, were used to image the object and take spectra for more detailed study.

This galaxy is about 6.9 billion years away from us. Its light was cast by a cluster of galaxies just 2.8 billion years old. To get the lensed images of SGAS J143845+145407, it had to be aligned precisely behind the cluster from Hubble’s perspective.

What have astronomers learned about this galaxy?

The team of astronomers who focused the HST on this galaxy discovered that the magnified view of SGAS J143845+145407 allowed them to obtain details of star formation in this galaxy. Without a lens, seeing this galaxy is a challenge. Thanks to its lens, astronomers can study individual star forming regions at a fairly high resolution. It turns out that star birth activity is taking place across large regions of the galaxy. Additionally, astronomers were able to clearly discern a two-armed structure in the galaxy. They call her a “grand design” spiral, which means she has well-defined arms. This galaxy also has a very red core and bluer emission clusters scattered in the spiral arms.

The massive amounts of star formation in the spiral arms of this galaxy strongly suggest that most (if not all) of the LIRGs have large-scale (perhaps even galaxy-wide) star formation bursts. ). If you compare them to the galaxies of the current universe, the difference is striking. Local universe galaxies can have very intense star forming nodes, but their scale is smaller than star forming regions in LIRGs.

Aim for victory

HST and JWST will continue to be the instruments of choice for studying lensed objects in the distant universe. While some are studied from the ground, those furthest from the early universe need the power of orbiting telescopes.

For more information

Hubble captures a mirror galaxy
Lens pattern and source reconstruction reveal morphology and distribution of star formation in cold spiral LIRG SGAS J143845.1+145407

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