ESO’s Very Large Telescope (VLT) has imaged the result of an amazing cosmic collision: the galaxy NGC 7727 in the constellation Aquarius. This giant was created from the merger of two galaxies, an event that began about a billion years ago. At its center is the closest pair of supermassive black holes that we know of. The two objects will eventually merge into an even more massive black hole.
Just as you can bump into someone on the street, so can galaxies. But while the interaction between galaxies is much more intense than a collision on a busy street, their individual stars do not collide quickly because the distances between stars are too large for their size. Instead, the galaxies dance around each other, as gravity creates tidal forces that dramatically change the appearance of both dancing partners. Before they merge into a new galaxy, the “tails” of stars, gas and dust circulate around the galaxies. This results in the beautifully irregular and asymmetric shape we see with NGC 7727. The dramatic effects of this cosmic collision are clearly visible in this image of the galaxy captured using FOcal Reducer and Spectrograph 2 (FORS2) on ESO’s VLT. Although the galaxy has been previously captured by another ESO telescope, this new image shows more intricate details, both in the galaxy itself and in its faint tails surrounding it.
This VLT image shows the tangled paths that formed when the two galaxies merged, pulling stars and dust together, creating amazingly long “arms” around NGC 7727. Parts of these arms are star-dotted, which appear as bright blue-purple spots in this picture. The image shows another trace of the galaxy’s dramatic past: the two bright blobs at its centre. The core of NGC 7727 still consists of two separate galactic cores, each containing a supermassive black hole. About 89 million light-years from Earth, this is the closest pair of supermassive black holes known.
The black holes of NGC 7727 appear in the sky only 1,600 light-years away. It’s expected to coalesce within 250 million years – a blink of an eye by astronomical standards. The merger will create a heavier black hole. The search for such hidden supermassive black holes is expected to receive a major boost when ESO’s Very Large Telescope (ELT) in Chile’s Atacama Desert becomes operational later this decade. With ELT, we can expect more such discoveries at the centers of galaxies.
Our galaxy, which also has a supermassive black hole at its center, is experiencing a similar merger with its nearest large neighbor, the Andromeda Galaxy, in billions of years. The resulting galaxy may look like the cosmic dance we see now in NGC 7727. The image shown here can give us a glimpse into the future.
This image was taken as part of ESO’s “Cosmic Gems” program – an initiative that uses ESO telescopes to image interesting, intriguing or visually appealing objects for educational or advertising purposes. This program uses Telescope Time and is not suitable for scientific observations. In the event that the collected data can also be used for scientific purposes, it is also made available to astronomers through the ESO Scientific Archive.
The European Southern Observatory (ESO) allows scientists from around the world to discover the secrets of the universe for the benefit of all. We design, build and operate world-class observatories that astronomers use to answer exciting questions, spread fascination with astronomy, and foster international cooperation in astronomy. Founded in 1962 as an intergovernmental organization, ESO is now supported by 16 member states (Belgium, Denmark, Germany, Finland, France, Ireland, Italy, Netherlands, Austria, Poland, Portugal, Spain, Czech Republic, United Kingdom, Sweden and Switzerland) and host country Chile, with Australia as a strategic partner. ESO’s headquarters, visitor center and planetarium, ESO Supernova, are located near Munich, Germany, but our telescopes are located in the Chilean Atacama Desert – a beautiful place with unique conditions for observing the sky. ESO operates three observation sites: La Silla, Paranal and Chajnantor. The Paranal includes the Very Large Telescope and the Very Large Interferometer Telescope, as well as two scanning telescopes: VISTA for infrared and VST for visible light. In Paranal, ESO will also house 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 in Chajnantor, two facilities that monitor the sky in the millimeter and below-millimeter range. At Cerro Armazones, near Paranal, we are building the “world’s largest eye” – ESO’s Very Large Telescope. From our offices in Santiago, Chile, we support our activities in the host country and cooperate with Chilean partners and the Chilean community.
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