Little Red Dot Abell2744-QSO1a (NIRCam image with NIRSpec IFU velocity map)

An image detail from Webb’s NIRCam shows the Little Red Dot Abell2744-QSO1, gravitationally lensed by Abell 2744, an enormous mega-cluster of galaxies also known as Pandora’s Cluster.

Pulled out to the right is a map showing the speed that gas is moving toward or away from the telescope (rotational velocity) in different parts of QSO1. The map was made with data collected using NIRSpec’s integral field unit (IFU), a combination of camera and spectrograph. The IFU gathers an image along with 900 spectra from a square patch of sky 3 arcseconds by 3 arcseconds, creating maps showing differences in brightness of thousands of wavelengths between 0.6-micron and 5.3-micron light across the object. The gas velocity is calculated based on Doppler shift: the colours are shifted slightly toward shorter (bluer) wavelengths where material is moving toward us, and longer (redder) wavelengths where it is moving away.

The Webb data shows that the glowing gas has Keplerian rotation: it is orbiting a central point in the same way that planets orbit a star. This means that most of the mass of QSO1 must reside in a single point in the centre, i.e., a black hole. Because the velocity of the orbiting gas follows very simple laws of gravity, the data can then be used to calculate the mass of the black hole: It appears to be 50 million solar masses, or 50 million times the mass of our Sun. This is about two-thirds of the entire mass of QSO1.

[Image description: Left: Space telescope image shows small, red, circular object outlined with white square. Scale bar in bottom left corner labeled 1 arcsecond shows that image is about 4 arcseconds across and object is about 0.4 arcseconds across. Right: Enlarged view of Little Red Dot overlaid with dumbbell-shaped array of pixels ranging in colour from blue to orange. Dumbbell shape is vertical, and pixels are oriented at 45 degrees. Below pixels is blue to orange scale bar showing that colour of each pixel is related to gas velocity in kilometres per second. Left side of scale bar grades from blue (labeled 20) to gray (labeled 0). Blue arrow pointing left from 0 to 20 beneath left (blue) side of scale bar is labeled toward. Orange arrow pointing right from 0 to 20 beneath the right (orange) side labeled away. Pixels on lower half of dumbbell shape are blue to gray.]