The Hubble team has released a beautiful image of Pismis 26, an ancient globular cluster in the constellation of Scorpius.
This Hubble image shows the 12-billion-year-old globular cluster Pismis 26. Imag credit: NASA / ESA / R. Cohen, Rutgers the State University of New Jersey / Gladys Kober, NASA / Catholic University of America.
Globular clusters are densely packed systems of stars, gravitationally bound into a single structure between 100 and 200 light-years across.
They contain hundreds of thousands or perhaps a million stars. The large mass in the rich stellar center of a cluster pulls the stars inward to form a ball of stars.
Globular clusters are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation.
It is thought that every galaxy has a population of globular clusters. Our Milky Way Galaxy hosts about 150-180 such objects and a few more are likely to exist hidden behind the Galaxy’s thick disk.
The globular cluster Pismis 26 was discovered by the Armenian-Mexican astronomer Paris Pişmiş at Tonantzintla Observatory in Mexico in 1959.
Also known as Tonantzintla 2 or Ton 2, the cluster is located 26,700 light-years away in the constellation of Scorpius.
It resides near the Milky Way’s bulge, which is an area near the center of our Galaxy that holds a dense, spheroidal grouping of stars that surrounds a black hole.
Due to its location within the dust-heavy bulge, a process called reddening occurs, where dust scatters shorter wavelength blue light while longer wavelength red light passes through.
The Hubble astronomers studied visible and infrared light from Pismis 26 to determine the cluster’s reddening, age, and metallicity.
“The stars of Pismis 26 have high metallicity, meaning they contain a high fraction of elements heavier than hydrogen and helium, the most abundant elements in the Universe,” they said.
“Specifically, the stars are rich in the element nitrogen, which is typical of stars in bulge clusters and has led scientists to believe that populations of differently-aged stars are present in the cluster.”
“Pismis 26 has also likely lost a sizable portion of its mass over time due to a gravitational force called the strong inner galaxy tidal field, which the inner galaxy exerts on star clusters in the galactic bulge, causing their outer layers to pull away.”
“We estimate the age of the cluster to be 12 billion years old.”
