2023-09-08 11:04:42
Globular cluster Terzan 12 – ESA
MADRID, 8 Sep. (EUROPA PRESS) –
The bright globular cluster Terzan 12, a vast and closely knit collection of stars, fills the frame of this image from the NASA/ESA Hubble Space Telescope.
The location of this globular cluster, deep in the Milky Way in the constellation Sagittarius, means it is shrouded in gas and dust that absorb and alter the starlight emanating from Terzan 12.
This star-studded stellar census comes from a series of observations aimed at systematically exploring the relatively few globular clusters toward the center of our galaxy, such as Terzan 12, located about 15,000 light years from Earth.
Globular clusters are not uncommon in the Milky Way. About 150 are known, most in its outer halo, and Hubble has revolutionized their study since its launch in 1990. However, examining clusters like Terzan 12, heavily obscured by interstellar dust, is complicated by the resulting reddening of the light, reports the ESA.
When starlight passes through an interstellar cloud, it can be absorbed and scattered by dust particles. The intensity of this scattering depends on the wavelength of the light, with the shorter wavelengths being those that are scattered and absorbed most strongly. This means that the blue wavelengths of starlight are less likely to pass through a cloud, which makes the stars in the background appear redder than they really are.
Astronomers refer to the color change caused by the scattering and absorption of starlight (appropriately) as reddening, and it is responsible for the vibrant range of colors in this image. Relatively clear stars glow brightly in white and blue, while creeping tendrils of gas and dust cover other large portions of Terzan 12, giving the stars an ominous red hue. The more dust there is along our line of sight to the cluster, the redder the starlight becomes.
A similar effect is responsible for the spectacular pink hues of sunsets here on Earth. The atmosphere preferentially scatters shorter wavelengths of light, which is why the sky appears blue. As the sun sinks into the sky, the sunlight has to pass through more of the atmosphere, which means that more and more blue light is scattered and the sunlight takes on a characteristic red-gold tone.
Some of the stars in the photo have completely different colors than their close neighbors. The brightest red stars are bloated, aging giants, many times larger than our Sun. They are located between Earth and the cluster. Only a few can actually be members of the group. The hot, very bright blue stars are also found along the line of sight and not within the cluster, which only contains aging stars.
The reddening of stars often poses problems for astronomers, but the scientists behind this observation of Terzan 12 were able to avoid the effect of gas and dust by comparing the new observations made with the clear view of the Advanced Survey Camera and the wide field 3 with pre-existing images. Their observations should shed light on the relationship between age and composition in the innermost globular clusters of the Milky Way. comparable to astronomers’ understanding of clusters spread throughout the rest of our galaxy.
The Terzan clusters suffer a kind of astronomical identity crisis: in reality there were only 11 clusters discovered by the Turkish-Armenian astronomer Agop Terzan. The confusion is due to a mistake made by Terzan in 1971, when he rediscovered Terzan 5 (a cluster he had already discovered and reported in 1968) and called it Terzan 11. Terzan attempted to correct the mistake by him, but the confusion caused has persisted. In scientific studies since then, astronomers finally settled on the strange convention that Terzan 11 does not exist.
Losing and then rediscovering astronomical objects is surprisingly common, even in our own Solar System. Minor planets, such as asteroids and dwarf planets, are often detected and then missed because their orbits cannot be determined from only a small handful of observations, adds the ESA statement.
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