This month’s NASA/ESA/CSA James Webb Space Telescope Image of the Moon gives us a two-in-one look at new stars – with possible planets!
This view highlights Webb’s views of the protoplanetary discs Tau 042021 (left) and Oph 163131 (right), otherwise known by the catalog numbers 2MASS J04202144+2813491 and 2MASS J16313124-2426281, respectively. Tau 042021 is located about 450 light-years from Earth in the constellation Taurus, while Oph 163131 sits 480 light-years away in Ophiuchus.
Protoplanetary discs like this form around newborn stars. When most of the gas in the larger molecular cloud collapses to form a star, unburnt gas and dust are left around the star in a dense disc. Over time, this dust also collides and collapses, slowly forming planets that can become planets. Planetesimals that cannot make the jump to a full planet are left behind as asteroids and comets that orbit the star. The gas not used up by this process is blown away by the radiation of the new star over tens of millions of years, destroying the protoplanetary disc. This is how our Solar System formed in the past, creating the stars, comets, gas giants and terrestrial planets we know today. By observing other protoplanetary discs from earlier ages, we can determine how this process worked for our Solar System, and how the different types of planets we see throughout the galaxy might have formed.
The unique thing that these two objects have in common is that, when we see them from our site and Webb, they face the edge of the disc facing us. This means that the bright light from the small central star is mostly blocked, and we see the fine dust that has come out of the disc as a nebula above and below the disc, illuminated by light reflected from the star. This is not only a beautiful sight, which produces these images similar to the spinning peaks of rainbow color in space, it is important for learning how these discs that make up the planet are formed. The distribution of dust within the disc, within it and above or below it, strongly affects where and how planets can form.
These images were created using data from Webb’s NIRCam and MIRI instruments, as part of Webb program #2562 (PI F. Ménard, K. Stapelfeldt). With the wide infrared sensitivity of these two cameras, Webb is able to monitor dust of different sizes throughout the disc. The red, orange and green colors of the discs in these images indicate different sizes of dust grains as well as molecules such as hydrogen (H2), carbon monoxide (CO) and polycyclic aromatic hydrocarbons (PAHs).
Both images also include data from the NASA/ESA Hubble Space Telescope, which shows visible light, particularly from the central star, showing fine dust particles. The Oph 163131 image also includes views from the Atacama Large Millimeter/submillimeter Array (ALMA). Where the Hubble and Webb images each contain dust only a few micrometers across, ALMA sees larger dust grains of about a millimeter in size, centered in the central plane of the disc. This can create the right conditions for the grains to continue to grow and form planets. In fact, the ALMA data for Oph 163131 shows a gap in the inner disc, which may be evidence that the planet is forming and removing surrounding dust.
[Image Description: Two images of protoplanetary discs side-by-side. The left image shows a dark horizontal band covering the star, with broad, colourful, conical outflows above and below it, and a narrow jet pointing directly up and down from the star. The right image shows the star within a yellow dusty disc, with scattered dust creating purple lobes above and below the disc. Each is on a black background with several galaxies or stars around it.]
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