We turn our eyes further out into the galaxy this week, toward the heart of the Milky Way, distant stars and supernovae, and a wandering comet due to return in less than 40 years.
Sunrise on Mars
This image, captured by NASA's Perseverance rover using the Left Navcam at around 7:20 a.m. local time on 4 September 2022, shows what sunrise looks like on Mars. Dust in the Martian atmosphere scatters blue light near the Sun to give it a blueish halo (even though most of the rest of the sky is redder).
Tycho's Supernova
In November 1572, Danish astronomer Tycho Brahe was among those who noticed a new bright object in the constellation Cassiopeia. Astronomers now know that Tycho's new star was not new at all. Rather it signaled the death of a star in a supernova, an explosion so bright that it can outshine the light from an entire galaxy. This particular supernova was a Type Ia, which occurs when a white dwarf star pulls material from, or merges with, a nearby companion star until a violent explosion is triggered. The white dwarf star is obliterated, sending its debris hurtling into space.
NASA's Chandra X-ray Observatory reveals an intriguing pattern of bright clumps and fainter areas in Tycho. To emphasize the clumps in the image and the three-dimensional nature of Tycho, scientists selected two narrow ranges of X-ray energies to isolate material (silicon, colored red) moving away from Earth, and moving towards us (also silicon, colored blue). The other colors in the image (yellow, green, blue-green, orange and purple) show a broad range of different energies and elements, and a mixture of directions of motion. In this composite image, Chandra's X-ray data have been combined with an optical image of the stars in the same field of view from the Digitized Sky Survey.
Zeta Oph: The Runaway Star
Like a ship plowing through cosmic seas, runaway star Zeta Ophiuchi produces the arcing interstellar bow wave or bow shock seen in this stunning infrared portrait. In the false-color view, bluish Zeta Oph, a star about 20 times more massive than the Sun, lies near the center of the frame, moving toward the left at 24 kilometers per second. Its strong stellar wind precedes it, compressing and heating the dusty interstellar material and shaping the curved shock front.
What set this star in motion? Zeta Oph was likely once a member of a binary star system; its companion star was more massive and, hence, shorter-lived. When the companion star exploded as a supernova, catastrophically losing mass, Zeta Oph was flung out of the system.
About 460 light-years away, Zeta Oph is 65,000 times more luminous than the Sun and would be one of the brighter stars in the sky if it weren't surrounded by obscuring dust. The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi. In January 2020, NASA placed the Spitzer Space Telescope in safe mode, ending its 16 successful years of exploring the cosmos.
Halley's Comet and the Milky Way
Happy birthday, Edmond Halley, after whom Comet 1P is named. While he may have been the first to understand the comet's periodic orbit, astronomers had recorded seeing the icy body as early as 240 BCE. We last saw Halley's Comet in our skies back in 1986, and this picture was taken by the European Southern Observatory. The comet will return at its perihelion - closest point in its orbit to the Sun - in 2061. In the meantime, enjoy not one but two annual meteor showers that occur as a result of Halley's orbit -- the Eta Aquariids in May and the Orionids in October.
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