Globular cluster Terzan 5

Many enjoy searching for the brilliant Perseids or the majestic Milky Way, but the universe holds more discreet treasures, jewels that, although difficult to see, tell fascinating stories about the origin of our own galaxy. One of those treasures is the globular cluster Terzan 5.

What is Terzan 5

Discovered by Turkish-French astronomer Agop Terzan in the 1960s, Terzan 5 is not a typical globular cluster.

Globular clusters are enormous spheres composed of hundreds of thousands of stars, as old as the cosmos, that revolve around the core of a galaxy.

However, Terzan 5 is different. It is hidden in the central bulge of the Milky Way, a dense area filled with dust that blocks most of its light, making it extremely difficult to detect, even from the world's most crystalline skies.

Lo que hace especial a Terzan 5 no es su resplandor, sino su estructura. A diferencia de la mayoría de los cúmulos globulares, que poseen estrellas de una sola edad, Terzan 5 contiene al menos dos grupos estelares con edades y composiciones químicas muy diferentes.

Algunas de sus estrellas son extremadamente antiguas, con más de 12 mil millones de años (casi la edad del universo), mientras que otras son «jóvenes», con aproximadamente 4.5 mil millones de años.

Terzan 5, a cosmic fossil

This age difference has led astronomers to a surprising deduction:

Terzan 5 could be a "cosmic fossil" or the vestige of one of the primordial components that came together to shape the central bulge of the Milky Way in its beginnings.

Rather than being a simple globular cluster, Terzan 5 is thought to be the surviving core of a dwarf galaxy or a fragment of dark matter that our Milky Way absorbed billions of years ago.

Funciona como una cápsula del tiempo estelar, que conserva en su interior las marcas de eventos clave en la formación de nuestra galaxia. Analizarlo nos permite asomarnos al pasado remoto y entender mejor cómo la Vía Láctea evolucionó desde un conjunto de estructuras menores hasta la imponente espiral que observamos hoy.

Video credit: Credit: Credit: Nick Risinger (skysurvey.org)/DSS/Hubble. | Music: Johan B. Monell

These are the physical characteristics of Terzan 5:

Distance: It is located about 25,000 light years away from Earth, in the constellation of Sagittarius, right in the direction of the galactic center, about 5,000 light years from its center.

Size: Despite the number of stars it contains, it is relatively compact, with a radius of almost 3 light years. This means that its stars are very close to each other, much closer than we are used to seeing in other globular clusters.

Mass: It is estimated at 2 million times the mass of our Sun.

Stellar population: Although it is very difficult to determine the quantity due to the opacity of star dust, it is home to hundreds of thousands of stars, including neutron stars and pulsars.

Why is Terzan 5 so special?

Apart from hosting two populations of stars and being a good candidate that helps us obtain information about the origins and formation of our Milky Way, pulsars, neutron stars and x-ray sources await within it.

Terzan 5 is known to be a true "nest" of pulsars, with more than 30 detected to date, making it one of the globular clusters with the highest density of these objects in the Milky Way.

Among them are some of the fastest pulsars in the galaxy, known as millisecond pulsars, which spin at astonishing speeds of hundreds of times per second.

Pulsars are neutron stars, the ultradense remains of massive stars that have collapsed after a supernova, that rotate rapidly and emit beams of electromagnetic radiation, acting as cosmic beacons that we can detect.

Among them, PSR J1748−2446ad stands out especially.

Discovered in 2004 by Jason W. T. Hessels, it is the fastest pulsar known so far, spinning at an astonishing speed of 716 times per second (716 Hz), or in other words, 42,960 revolutions per minute.

Additionally, Terzan 5 is a notable source of X-ray emissions, many of which come from exotic binary systems.

In these systems, a neutron star captures material from a nearby companion star. This stolen material forms an accretion disk around the compact object, where the gas is heated to extreme temperatures of millions of degrees, emitting intense X-rays.

Their high stellar density favors the formation of these binary systems, since gravitational interactions between stars can generate tight pairs that evolve towards these configurations.

Recent telescope studies have revealed that it houses dozens of X-ray sources, making it a natural laboratory for investigating the physics of compact objects and the extreme conditions of the galactic bulge.

Therefore, although observing Terzan 5 directly is an almost impossible challenge due to the dust that hides it in the galactic bulge, its existence and what it teaches us are a fascinating testimony of the enigmas that the cosmos still holds.

As we contemplate the starry nights, the thought that a cosmic relic from our galaxy's childhood is so close, yet so well hidden, and that it acts as a natural laboratory for pulsars and X-ray sources, awakens a deep admiration for the night sky.

So, the next time you look up at the Milky Way, remember that in the dense heart of our galaxy lies a silent witness to the Milky Way's chaotic origins.

Astronomy not only invites us to observe, but also to unravel the extraordinary stories that the stars and their cosmic relics whisper to us through time.