A wreath of star formation in Pegasus
ESA published this original article on December 21, 2022. Read the original article here. Edits by EarthSky.
A wreath of star formation
The luminous, face-on spiral galaxy NGC 7469 is at the heart of Webb’s picture of the month for December. Approximately 90,000 light-years in diameter, the galaxy lies roughly 220 million light-years from Earth in the constellation Pegasus.
The Great Observatories All-sky LIRGs Survey (GOALS) recently studied this spiral galaxy. The goal of “GOALS” is to study the physics of star formation, black hole growth and feedback in four nearby, merging luminous infrared galaxies. Other galaxies that are a part of the survey include previous ESA Webb Pictures of the Month II ZW 096 and IC 1623.
Starry spiral NGC 7469
NGC 7469 is home to an active galactic nucleus (AGN), which is an extremely bright central region dominated by the light emitted by dust and gas as it falls into the galaxy’s central black hole. This galaxy provides astronomers with the unique opportunity to study the relationship between AGNs and starburst activity. That’s because NGC 7469 hosts an AGN that is surrounded by a starburst ring at a distance of a mere 1,500 light-years.
While NGC 7469 is one of the best studied AGNs in the sky, the compact nature of this system and the presence of a great deal of dust have made it difficult for scientists to achieve both the resolution and sensitivity needed to study this relationship in the infrared. Now, with Webb, astronomers can explore the galaxy’s starburst ring, the central AGN, and the gas and dust in between.
New discoveries in the wreath of star formation
Webb’s MIRI, NIRCam and NIRspec instruments obtained images and spectra of NGC 7469 in unprecedented detail. The GOALS team uncovered a number of discoveries about the object. This includes very young star-forming clusters never seen before and pockets of very warm, turbulent molecular gas.
The team also saw direct evidence for the destruction of small dust grains within a few hundred light-years of the nucleus. This proves that the AGN is impacting the surrounding interstellar medium. Furthermore, highly ionized, diffuse atomic gas seems to be exiting the nucleus at roughly 4 million miles per hour (6.4 million kilometers per hour). This speedy gas is part of a galactic outflow that scientists previously identified from the ground, but now they see it in stunning detail with Webb. They expect to learn more of NGC 7469’s secrets as analysis of the rich Webb datasets continue.
Why is there a diffraction spike?
A prominent feature of this image is the striking six-pointed star that perfectly aligns with the heart of NGC 7469. Unlike the galaxy, this is not a real celestial object, but an imaging artifact known as a diffraction spike. In this case, the bright, unresolved galactic core causes the diffraction spike.
Diffraction spikes are patterns produced as light bends around the sharp edges of a telescope. Webb has three struts, with two angled at 150 degrees from its vertical strut. Plus, its primary mirror consists of hexagonal segments that each contain edges for light to diffract against. Engineers designed Webb’s struts so that their diffraction spikes partially overlap with those created by the mirrors. Both of these lead to Webb’s complex “star” pattern.
Bottom line: The Webb space telescope captured this image of the spiral galaxy NGC 7469 in Pegasus. You can see a wreath of star formation in the ring around the galaxy’s central black hole.