Galaxies merger produces a spectacular cosmic dance

ESO telescope captures an event that started around a billion years ago

ESO’s Very Large Telescope (VLT) has imaged the result of a spectacular cosmic collision — the galaxy NGC 7727. This giant was born from the merger of two galaxies, an event that started around a billion years ago. At its centre lies the closest pair of supermassive black holes ever found, two objects that are destined to coalesce into an even more massive black hole.

Just as you may bump into someone on a busy street, galaxies too can bump into each other. But while galactic interactions are much more violent than a bump on a busy street, individual stars don’t generally collide since, compared to their sizes, the distances between them are very large. Rather, the galaxies dance around each other, with gravity creating tidal forces that dramatically change the look of the two dance partners. ‘Tails’ of stars, gas and dust are spun around the galaxies as they eventually form a new, merged galaxy, resulting in the disordered and beautifully asymmetrical shape that we see in NGC 7727.

The galaxy NGC 7727 was born from the merger of two galaxies that started around a billion years ago. The cosmic dance of the two galaxies has resulted in the spectacular wispy shape of NGC 7727. At the heart of the galaxy, two supermassive black holes are spiralling closer to each other, expected to merge within 250 million years, the blink of an eye in astronomical time. This image of NGC 7727 was captured by the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument at ESO’s Very Large Telescope (VLT).

The consequences of this cosmic bump are spectacularly evident in this image of the galaxy, taken with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument at ESO’s VLT. While the galaxy was previously captured by another ESO telescope, this new image shows more intricate details both within the main body of the galaxy and in the faint tails around it.

In this ESO VLT image we see the tangled trails created as the two galaxies merged, stripping stars and dust from each other to create the spectacular long arms embracing NGC 7727. Parts of these arms are dotted with stars, which appear as bright blue-purplish spots in this image.

Also visible in this image are two bright points at the centre of the galaxy, another tell-tale sign of its dramatic past. The core of NGC 7727 still consists of the original two galactic cores, each hosting a supermassive black hole. Located about 89 million light-years away from Earth, in the constellation of Aquarius, this is the closest pair of supermassive black holes to us.

Close-up view of the two bright galactic nuclei, each housing a supermassive black hole, in NGC 7727, a galaxy located 89 million light-years away from Earth in the constellation Aquarius. Each nucleus consists of a dense group of stars with a supermassive black hole at its centre. The two black holes are on a collision course and form the closest pair of supermassive black holes found to date. It is also the pair with the smallest separation between two supermassive black holes — observed just 1600 light-years apart in the sky. The image was taken with the MUSE instrument on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile.

The black holes in NGC 7727 are observed to be just 1600 light-years apart in the sky and are expected to merge within 250 million years, the blink of an eye in astronomical time. When the black holes merge they will create an even more massive black hole.

The search for similarly hidden supermassive black hole pairs is expected to make a great leap forward with ESO’s upcoming Extremely Large Telescope (ELT), set to start operating later this decade in Chile’s Atacama Desert. With the ELT, we can expect many more of these discoveries at the centres of galaxies.

Our home galaxy, which also sports a supermassive black hole at its centre, is on a path to merge with our closest large neighbour, the Andromeda Galaxy, billions of years from now. Perhaps the resulting galaxy will look something similar to the cosmic dance we see in NGC 7727, so this image could be giving us a glimpse into the future.

Just as people at a busy crossroad may accidentally bump into each other, so too can galaxies in the Universe! But in this case, the outcome is more dramatic than a small nudge. When two galaxies clash, they merge into each other, giving birth to a new, bigger one. One example is the NGC 7727 galaxy, shown in this image from ESO’s VLT Survey Telescope (VST) in Chile. Located 89 million light-years away from Earth in the constellation Aquarius, NGC 7727 is believed to be the result of a clash between two galaxies that occurred about one billion years ago. The consequences of this tremendous cosmic bump are still evident in the peculiar, irregular shape of NGC 7727 and the streams of stars in its outer regions. The image was taken in visible light as part of the VST-ATLAS survey. The goal of the survey is to map a vast region of the Southern Sky — so large you could fit about 19,000 full moons in it! By studying the galaxies in this region, astronomers aim to shed new light on the nature of dark energy, the mysterious force permeating the Universe and causing its accelerating expansion.

This image was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner.

This image from the Digitized Sky Survey (DSS) shows the region of the sky around NGC 7727, a galaxy located 89 million light-years away from Earth in the constellation Aquarius. The galaxy is the bright spot in the centre. NGC 7727 is home to the closest pair of supermassive black holes to Earth found to date. It is also the pair with the smallest separation between two supermassive black holes — observed to be just 1600 light-years apart in the sky.

ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope.

Also, at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. (ESO)