Warped Galaxies

Can you match each galaxy in the top row of figure 1 with its warped counterpart in the bottom row? For example, is the warped version of galaxy A in box D, E, or F? Answers are below.

Such galaxy warping occurs naturally in nature in a phenomenon called strong gravitational lensing. The gravity of matter in front of a more distant galaxy, either dark or normal matter, bends and twists the galaxy's light, resulting in wacky shapes and sometimes multiple versions of the same galaxy. It's like seeing a galaxy in a funhouse mirror. Scientists use these natural lenses to make maps of dark matter, an invisible substance permeating our cosmos. The lenses also help in the study of dark energy, an even more mysterious substance thought to be pushing universe apart at increasing speeds.

This quiz demonstrates extreme cases of gravitational lensing. The warped images have been simulated from original images of galaxies taken by NASA's Hubble Space Telescope. Galaxy E shows what is called an "Einstein ring," named after Albert Einstein, who discovered that gravity bends light. In this case, the mass of one body, a lump of dark matter, has twisted the galaxy's light into a ring. In the other two cases, two lensing sources create double-ringed structures.

In reality, most lenses are not this obvious. In what is called weak gravitation lensing, the effects are subtle and hard to tease out. Scientists have created a competition called GREAT3, which stands for GRavitational lEnsing Accuracy Testing 3, to improve methods for measuring weak lensing. Data scientists from an assortment of fields, including machine learning, are invited to solve galaxy puzzles, in which tiny lensing affects have been artificially introduced by the organizers of the challenge. The goal is to figure out what the lensing affects are, and in doing so, help develop new tools for probing the dark side of our cosmos.

Image credit: NASA/JPL-Caltech/UCL

Answers to quiz: A matches F; B matches D; and C matches E.

Note: For more information, see Scientists Seek Other Scientists for Cosmology Problem

ALMA/HST Images of Gravitationally-Lensed Star-Forming Galaxies

This montage combines data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The ALMA images, represented in red, show the distant, background galaxies, being distorted by the gravitational lens effect produced by the galaxies in the foreground, depicted in the Hubble data in blue. The background galaxies appear warped into rings of light known as Einstein rings, which encircle the foreground galaxies.

Image credit: ALMA (ESO/NRAO/NAOJ), J. Vieira et al.

Note: For more information, see ALMA Rewrites History of Universe's Stellar Baby Boom.

Lone Planet Under a Cosmic Magnifying Glass

This artist's animation illustrates the technique used for finding free-floating, Jupiter-mass planets in space. Astronomers found evidence for 10 of these worlds, thought to have been ejected early on from their developing solar systems.

The movie begins by showing the busy, central region of our Milky Way galaxy, where the planets were found with a ground-based telescope. It then zooms in on a star that brightens. This brightening is due to the passage of an unseen, free-floating planet (and has been exaggerated here). As a planet just happens to cross in front of a more distant star, its gravity causes the starlight to warp, and this warping resulted in an overall brightening of the star as seen by the telescope. In this effect, called gravitational microlensing, the planet's gravity plays the role of a magnifying lens.

The next part of the animation shows a zoomed in view of what the microlensing of a star would look like if it could be seen at much higher resolution. The blue dot represents the planet, but has been enlarged to make it easy to see. The main star is the brightest dot in the center, shown amidst other smaller, red and yellow stars. As the planet passes by, its gravity causes light from the stars to split into multiple, mirrored and reversed images. When the planet is directly in front of the main star, that star's multiple images are stretched into arcs. The overall result is a temporary brightening of the star.

Astronomers refer to the circular shape that can be seen as the planet passes by the stars as an Einstein Ring. When a planet is directly in front of star, it will cause the starlight to bend into a full Einstein Ring. When the planet is near stars, it will cause the star images to either appear deflected away from the ring, or inverted and reversed within the ring.

The duration of the microlensing event will reveal the rough mass of the passing body. Jupiter-mass objects will cause a star to brighten more quickly, over just a day or two. A passing star would cause a more distant star to brighten over a period of weeks.

The overall density of stars, as well as the brightness of their inverted images within the Einstein ring, have been exaggerated in this animation to help show the effects of the gravitational lensing. It is very rare for one passing planet to distort the light from multiple stars at once.

The movie ends with an artist's conception of a free-floating, Jupiter-mass world.

The gravitational microlensing shown is based on simulation data from M. Freeman (University of Auckland, New Zealand).

Video credit: NASA

Note: For more information, see Free-Floating Planets May Be More Common Than Stars.