White Dwarf Migration in Globular Cluster 47 Tucanae

This diagram shows how white dwarfs, the burned-out relics of stars, are distributed in the ancient globular star cluster 47 Tucanae. The youngest white dwarfs are the hottest and bluest stars dwelling mostly in the cluster’s core, where the most massive stars reside. Shortly before collapsing to become white dwarfs, the stars shed most of their mass. Now, as lightweight white dwarfs, they interact gravitationally with more massive stars in the core. Through these gravitational encounters, the white dwarfs rob enough speed from their more massive cousins to begin migrating slowly outward from their home. During their journey, they become older and cooler white dwarfs, depicted in the orange dots. Eventually, the white dwarfs settle on the outskirts of the cluster, where the oldest, coolest, reddest white dwarfs reside.

Globular cluster 47 Tucanae

This NASA/ESA Hubble Space Telescope image shows a globular cluster known as NGC 104 — or, more commonly, 47 Tucanae, since it is part of the constellation of Tucana (The Toucan) in the southern sky. After Omega Centauri it is the brightest globular cluster in the night sky, hosting tens of thousands of stars. 

NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Central regions of 47 Tucanae seen in visible light and in the ultraviolet

These NASA/ESA Hubble Space Telescope images show the central region of 47 Tucanae, seen in visible light (top) and in ultraviolet light (bottom).

NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

NASA, ESA, and H. Richer and J. Heyl (University of British Columbia, Vancouver)

Using the ultraviolet capabilities of Hubble’s sharp-eyed Wide Field Camera 3, the astronomers traced populations of white dwarfs with a range of ages and positions. This made it possible, for the first time, to collect a census of young white dwarf stars beginning their migration from the crowded centre of an ancient star cluster to its less populated outskirts.

The globular cluster NGC 6388 observed by the European Southern Observatory

This image from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile shows NGC 6388, a dynamically middle-aged globular cluster in the Milky Way. NGC 6388 is a globular cluster at distance d ≃ 11.5 kpc (about 37,500 light-years) and with an estimated mass of 2.6 × 10⁶ M_⊙. 

ESO, F. Ferraro (University of Bologna)

The globular cluster NGC 6388, observed by Hubble

While NGC 6388 formed in the distant past (like all globular clusters, it is over ten billion years old), a study of the distribution of bright blue stars within the cluster shows that it has aged at a moderate speed, and its heaviest stars are in the process of migrating to the centre. 

NASA, ESA, F. Ferraro (University of Bologna)

Globular cluster Fornax 5

This Hubble Space Telescope image shows the globular cluster Fornax 5 in the dwarf galaxy Fornax. Its mean distance is 0.140 Mpc. Other name: ESO 356-SC 008. 

NASA, ESA, S. Larsen (Radboud University, the Netherlands)

Globular cluster Fornax 3

This NASA/ESA Hubble Space Telescope image shows the globular cluster Fornax 3 in the dwarf galaxy Fornax. Other names: NGC 1049, ESO 356-SC 003. 

NASA, ESA, S. Larsen (Radboud University, the Netherlands)

Globular cluster Fornax 2

This Hubble Space Telescope image shows the globular cluster Fornax 2 in the dwarf galaxy Fornax. Its distance is 0.138 Mpc (about 450,000 light-years). Other name: ESO 356-SC 001. 

NASA, ESA, S. Larsen (Radboud University, the Netherlands)

Globular cluster Fornax 1

This Hubble Space Telescope image shows the globular cluster Fornax 1 in the dwarf galaxy Fornax. Its distance is 0.142 Mpc (about 463,000 light-years). Other name: ESO 355-SC 029. 

NASA, ESA, S. Larsen (Radboud University, the Netherlands)

Fornax galaxy with four globular clusters marked

This is a Digitized Sky Survey 2 image of the dwarf galaxy Fornax. Highlighted here are four globular clusters found in the galaxy called Fornax 1, 2, 3 and 5. 

ESO/Digitized Sky Survey 2

Reconstructing the star birth environment in a globular cluster

Using state of the art computer simulations, a team of astronomers from the University of Bonn in Germany have found the first evidence that the way in which stars form depends on their birth environment. The team, based at the University of Bonn in Germany, publish their results in the journal Monthly Notices of the Royal Astronomical Society.

A Hubble Space Telescope image of the massive star cluster R 136 in the Large Magellanic Cloud. R136 is a potential birth site of much more massive stars, although unconfirmed, than observed in "normal" sites of present-day star formation. Credit: NASA, J. Trauger (JPL), J. Westphal (Caltech)

Messier 55, a swarming ball of stars in Sagittarius

A new image of Messier 55 from ESO's VISTA infrared survey telescope shows tens of thousands of stars crowded together like a swarm of bees. Besides being packed into a relatively small space, these stars are also among the oldest in the Universe. Astronomers study Messier 55 and other ancient objects like it, called globular clusters, to learn how galaxies evolve and stars age.

The ball of stars at the center of the globular cluster Messier 55. This is a partial view of the image obtained in infrared light with the VISTA survey telescope at ESO’s Paranal Observatory in Chile. Credit: ESO/J. Emerson/VISTA