for the James Webb Space Telescope
Below we highlight several science themes the NIRCam team will be exploring upon launch of JWST.
One of the greatest scientific discoveries of the 20th century was that the universe is expanding. The discovery came from the observation that all but the very closest galaxies in the universe appear to be moving away from Earth. This was done by measuring the displacement due to the Doppler effect of the spectroscopic lines of some common atoms within the spectra of these galaxies – such as hydrogen, oxygen, nitrogen, calcium, iron, and magnesium. This displacement is known as the redshift.
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What makes something a planet, a brown dwarf or a star? Generally, planets are less massive (<13 times as massive as Jupiter) and do not have enough central pressure to fuse deuterium, a form of hydrogen with an extra neutron. Stars are more massive (>80 times as massive Jupiter) and capable of fusing regular (neutron-free) hydrogen. The objects in between planets and stars are called brown dwarfs, which can burn only deuterium. However, the dividing lines between these objects are not always so clear – think about the controversy over how to classify Pluto, Kuiper Belt objects and dwarf planets in our own solar system. Another way to tackle this question is by how these objects form: are they made in a disk surrounding a star or do they collapse out of the gas in a star-forming cloud?
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Astronomers have known for some time that objects in the distant Kuiper Belt region of the solar system, whether small debris or large objects like Pluto and its moons, contain icy surfaces. The New Horizons flyby of 2015 captured Pluto’s icy surfaces in great detail, revealing them to be much more dynamic than originally expected. Even still, a good inventory of the ices present in the outer solar system has yet to be taken, and the evolution of the surface features remains poorly understood. It is as yet unknown whether these objects have fresh icy surfaces, perhaps resulting from damaged ices knocked off during a collision, or much older icy surfaces modified by cosmic rays and ultraviolet light from the sun. Both can cause chemical reactions, resulting in a darkening in color, as can be seen on objects throughout the Kuiper Belt region.
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