Hubble Captures Gravitational Lens Ahead of Roman Telescope Mission

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NASA has released a Hubble Space Telescope image of a gravitational lens, one of many such observations the agency is making in preparation for science with the upcoming Nancy Grace Roman Space Telescope. The picture shows a distant galaxy whose light is bent and magnified by a closer one.

What the image shows

The image shows a sweeping barred spiral galaxy, but NASA points to a gravitational lens in the lower-right corner as its main feature. There, a reddish elliptical galaxy in the foreground sits in front of a more distant galaxy whose light has been stretched into blue arcs.

The foreground galaxy is about 4.5 billion light-years away. The background galaxy lies roughly eight billion light-years distant, almost twice as far. The arrangement produces a large arc to the upper left of the foreground galaxy and a smaller, flipped image of the same background galaxy to the lower right, a configuration called an arc-counterarc pair.

Almost every object in the frame is a galaxy, apart from a few foreground stars. A tiny spiral to the left of the large one may be a satellite galaxy, comparable to the Large and Small Magellanic Clouds that orbit the Milky Way.

Why lensing matters for dark matter

Gravitational lensing occurs when the mass of a foreground object warps spacetime, bending and magnifying light from objects behind it. The more massive the foreground galaxy, the stronger the lens and the greater the bending. This makes lensing a central tool for studying dark matter, the invisible substance that accounts for most of the mass in the universe.

The visible matter in the foreground galaxy does not fully explain the degree of distortion seen in the background galaxy. Researchers can therefore use the distortion to estimate both the foreground galaxy's total mass and how much of it is dark matter. Astronomers are using Hubble's sharp images to build a computer model to analyse these dark matter-induced distortions more precisely.

Hubble and Roman as complementary instruments

Hubble observes mainly in visible and ultraviolet light, with some infrared coverage, and gives high-resolution views of individual objects. The Roman telescope will see mainly infrared wavelengths and some visible light, with a much wider field of view suited to panoramic surveys.

This lensing image is one of many gravitational lens observations Hubble has captured, and NASA describes the series as preparation for the science Roman will carry out.

Open questions

When the Nancy Grace Roman Space Telescope will begin its science operations?
How many lensing observations Hubble will ultimately contribute to the preparation effort?

Key facts

NASA's Hubble Space Telescope imaged a gravitational lens as part of preparations for the Nancy Grace Roman Space Telescope.

The foreground elliptical galaxy lies about 4.5 billion light-years away, while the background galaxy is about eight billion light-years distant.

The lensed background galaxy appears as a large arc and a smaller flipped counterpart, known as an arc-counterarc pair.

Astronomers use such distortions to calculate the mass of foreground galaxies and the dark matter they contain.

Hubble and Roman observe complementary wavelengths and fields of view.