Hubble finds that ghost light among galaxies stretches far back in time

Hubble finds that ghost light among galaxies stretches far back in time

These are Hubble Space Telescope images of two massive galaxy clusters called MOO J1014+0038 (left panel) and SPT-CL J2106-5844 (right panel). The artificially added blue color is interpreted from Hubble data that captured a phenomenon called intracluster light. This extremely faint glow traces a smooth scattering of light from stray stars scattered throughout the cluster. Billions of years ago stars were ejected from their parent galaxies and now drift through intergalactic space. Credit: NASA, ESA, STScI, James Jee (Yonsei University)

In giant clusters of hundreds or thousands of galaxies, countless stars wander among the galaxies like lost souls, giving off a ghostly haze of light. These stars are not gravitationally bound to any single galaxy in a cluster.

The nagging question for astronomers has been: how did the stars become so widely distributed in the cluster in the first place? Some competing theories include the possibility that the stars were stripped from a cluster’s galaxies, or were ejected after the galaxies merged, or that they were present in the early years of a cluster’s formation many billions of years ago.

A recent infrared survey by NASA’s Hubble Space Telescope, which looked for this so-called “intracluster light” sheds new light on the mystery. The new Hubble observations suggest that these stars have been roaming around for billions of years and are not the product of more recent dynamical activity within a cluster of galaxies that would separate them from normal galaxies.

The survey included 10 galaxy clusters up to nearly 10 billion light-years across. These measurements must be made from space because the faint light within the cluster is 10,000 times fainter than the night sky as seen from Earth.

The survey finds that the fraction of light within the cluster relative to the total light in the cluster remains constant, looking back billions of years in time. “This means that these stars were already homeless in the early stages of cluster formation,” said James Jee of Yonsei University in Seoul, South Korea. His results are being published in the January 5 issue of the journal Nature.

Stars can be scattered outside their galactic birthplace when a galaxy moves through the gaseous material in intergalactic space as it orbits the center of the cluster. In this process, drag pushes gas and dust out of the galaxy. However, based on the new Hubble survey, Jee rules out this mechanism as the main cause of star production within clusters. This is because the fraction of light within the array will increase over time until now if stripping is the main player. But that’s not the case in the new Hubble data, which show a constant fraction over billions of years.

Image of the galaxy clusters MOO J1014+0038 (left panel) and SPT-CL J2106-5844 (right panel) captured by Hubble’s Wide Field Camera 3, with color key, compass arrows and scale bar for reference . This image shows near-infrared wavelengths of light. The color key indicates which filters were used when collecting the light. The color of each filter name is the color used to represent the wavelength that passes through that filter. The compass chart shows the orientation of the object in the celestial sphere. North indicates the north celestial pole, which is not a fixed point in the sky, but currently lies near the star Polaris, in the circumpolar constellation Ursa Minor. Celestial coordinates are analogous to a terrestrial map, although east and west are transposed because we are looking up and not down. The scale bar is labeled in light years (ly) and parsecs (pc). Credit: NASA, ESA, STScI, James Jee (Yonsei University)

“We don’t know exactly what made them homeless. Current theories can’t explain our results, but somehow they were produced in large quantities in the early universe,” Jee said. “In their early formative years, galaxies may have been quite small and they bled stars very easily due to a weaker gravitational grip.”

“If we understand the origin of stars within clusters, it will help us understand the assembly history of an entire cluster of galaxies, and they can serve as visible tracers of the dark matter enveloping the cluster,” said Hyungjin Joo of Yonsei University, the first author. of paper. Dark matter is the invisible scaffolding of the universe that holds galaxies and galaxy clusters together.

If stray stars were produced through a relatively recent game of pinball between galaxies, they do not have enough time to disperse throughout the cluster’s gravitational field and therefore would not trace the distribution of the cluster’s dark matter. But if the stars were born in the first years of the cluster, they will be completely scattered throughout the cluster. This would allow astronomers to use the rogue stars to determine the distribution of dark matter throughout the cluster.

This technique is new and complementary to the traditional method of dark matter mapping by measuring how the entire array distorts light from background objects due to a phenomenon called gravitational lensing.

Intracluster light was first detected in the Coma cluster of galaxies in 1951 by Fritz Zwicky, who reported that one of his most interesting discoveries was the observation of faint, luminous intergalactic matter in the cluster. Because the Coma cluster, which contains at least 1,000 galaxies, is one of the closest clusters to Earth (330 million light years), Zwicky was able to detect the ghostly light even with a modest 18-inch telescope.

The near-infrared capability and sensitivity of NASA’s James Webb Space Telescope will greatly expand the search for stars within clusters deeper in the universe, and should therefore help solve the mystery.

More information: Myungkook Jee, Intracluster light is already abundant at redshift beyond unity, Nature (2023). DOI: 10.1038/s41586-022-05396-4.

Provided by ESA/Hubble Information Center

Citation: Hubble Finds Ghost Light Between Galaxies Extends Far in Time (2023, January 4) Retrieved January 5, 2023 from

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