In the northern sky, located 3,400 light-years in the constellation of Perseus, the Little Dumbbell Nebula is the 76th Messier object. Classified as a bipolar planetary nebula, it was the image that NASA, ESA, and the Space Telescope Science Institute (STScI) chose to celebrate the 34th anniversary of the launch of the Hubble Space Telescope. Aboard the Space Shuttle Discovery, Hubble was launched on April 24, 1990, with the STS-31 mission[1].
M76 is classified as a planetary nebula; name these types of objects received because of how they looked when observed with the early telescopes. Because some were round and with a bright star in their centers, these evoked the image of our Solar System when seen from afar.
The bright object at its center is indeed a star, a white dwarf star. It is the remnant of the star that, when young, must have had between 1 to 8 solar masses. However, the bright shell of glowing gas surrounding it, is material from the star itself, but that was ejected while in its Red Giant stage. The planetary nebula stage is one of the final stages in the life of a star.
The shapes we observe in planetary nebulas depend on the direction we observe them and also on the environment where the star evolves. Messier 76 looks like many other planetary nebulas, with two lobes expanding in opposite directions, but it also has some peculiarities that make it look special. In this case, M76 has a central bar-like shape, which is actually a ring around the central star, that when seen at an angle, looks like a bar with the longest axis crossing a line from 5:50 to 11:30 and the shortest axis going from 8:30 to 2:30. In this planetary nebula, the two lobes expand from either opening of the ring.
Astronomers believe that the ring was probably sculpted by the effects of a binary companion star, where the ejected gas and dust from the now central star created a thick disk of dust and gas along the plane of the companion's orbit. This companion star is not visible in the Hubble image, which means this companion might have been stripped of all its material and now probably became part of the central star[1].
The white dwarf in the center is very hot, about 250,000°F; quite hot when compared to the 9,930°F of our Sun. This is the core of a star that has shed all its outer layers and has run out of fuel to produce energy through fusion. Now, it is supported only by the pressure of the electrons, which when confined to a small volume, have a large kinetic energy that prevents the star from collapsing further[2][3].
The Little Dumbbell Nebula, known also as the Cork Nebula or Barbell Nebula, has two lobes that are the result of hot gas escaping at about two million miles per hour. The material that the star ejected when it was a Red Giant now glows due to the intense radiation from the central star that ionizes this material and the hot gas that moves at a higher speed and plows it on its way out. The entire nebula is expected to vanish in about 15,000 years[2].
M76 was observed in the early years of Hubble with the Wide Field and Planetary Camera 2, and now, for its 34th anniversary, the powerful Wide Field Camera 3 took another snapshot in the near-infrared and visible light to further understand the distribution and evolutionary states of this and other planetary nebulas.
Hubble after 34 years of service
Hubble is one of the most productive science observatories. With its discoveries, it has changed the books of astronomy and our understanding of the universe. With 1.6 million observations of over 53,000 astronomical objects made to date, the Mikulski Archive for Space Telescopes at STScI is still an incredible resource for new research and analysis for astronomers around the world. Since 1990, 44,000 science papers have been published from Hubble observations, making the Hubble Space Telescope the most scientifically productive space astrophysics mission in NASA history.[2].
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