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Ghostly galaxy without dark matter discovered



  Galaxy without dark matter
Source: Gemini Observatory / NSF / AURA / Keck / Jen Miller

Galaxies and dark matter go hand in hand; Usually you can not find one without the other. When researchers discovered a galaxy known as the NGC1052-DF2, they were shocked.

"Finding a galaxy without dark matter is unexpected, because this invisible, mysterious substance is the most dominant aspect of galaxy every galaxy," said lead author Pieter van Dokkum of Yale University. "For decades, we thought that galaxies start out as dark matter, and then everything else happens: gas falls into the dark matter halos, gas turns into stars, they build up slowly, then galaxies end up like the Milky Way galaxy, NGC1052-DF2 Standard notions on how we form galaxies. "

The study, published in the March 29 issue of the journal Nature, collected data from Gemini North and the WM Keck Observatory on Maunakea, Hawaii, the Hubble Space Telescope, and other telescopes Around the World

Astronomers classify NGC1052-DF2 as an ultra-diffused galaxy, a relatively new type of galaxy that was first discovered in 2015, due to its size and weak appearance. These barely visible galaxies are surprisingly commonplace. But no other galaxy of this type discovered so far lacks dark matter.

"NGC 1052-DF2 is a curiosity, even among this unusual class of galaxies," said Shany Danieli, a graduate student at Yale University

Van Dokkum and his team first discovered NGC1052-DF2 with the Dragonfly Telephoto Array , a tailor made telescope in New Mexico that found these ghostly galaxies. The comparison of NGC1052-DF2 with images from the Dragonfly Tele-Array and the Sloan Digital Sky Survey (SDSS) showed a strong contrast. The Dragonfly images show a faint "blob-like" object, while SDSS data shows a collection of relatively bright punctate sources.

To further examine this inconsistency, the team dissected the light from several of the bright sources in NGC1052-DF2 using the Deep Imaging Multi-Object Spectrograph (DEIMOS) and the Keck Observatory's Low-Resolution Imaging Spectrometer (LRIS) for identification of 10 globular clusters. These clusters are large compact groups of stars orbiting the galactic nucleus.

The spectral data of the Keck telescopes showed that the globular clusters move much slower than expected. The slower the objects move in a system, the less mass there is in this system. The team's calculations show that the total mass in the galaxy can be assigned to the mass of stars, meaning that there is almost no dark matter in NGC1052-DF2.

"If there is dark matter at all, it is very little," van Dokkum explained. "The stars in the galaxy can be responsible for the entire mass, and there seems to be no room for dark matter."

"Keck is in a very small group of telescopes that could even try these observations because you need a large telescope to measure these exact speeds," van Dokkum added. "Keck also has some of the best spectrographs in the world to measure the speed of weak objects, so we had the opportunity to check and make sure that we had the same result within the uncertainties, and that gave us the confidence that we did things Do it right. "

To explore deeper into this unique galaxy, the team used the Gemini North Multi-Object Spectrograph (GMOS) to capture detailed images of NGC1052-DF2, evaluate its structure, and confirm its structure that the galaxy shows no signs of interaction with other galaxies.

"Without the Gemini images that analyze the galaxy's morphology, we would not have had any connection for the rest of the data," Danieli said. "Gemini's confirmation that NGC1052-DF2 currently does not interact with any other galaxy will help us answer questions about the conditions of its birth."

The team's results show that dark matter is separable from galaxies.

shows that dark matter is real – it has its own existence alongside other components of galaxies, "said van Dokkum.

The globular clusters and atypical structures of NGC1052-DF2 have confused astronomers who determine the conditions of this galaxy 19659004] "It's like taking a galaxy and only having the star wreath and the globular clusters and somehow forgetting to do everything else," van Dokkum said. "There is no theory that predicts these types of galaxies , The galaxy is a complete mystery because it's all weird about it. How you actually form one of these things is completely unknown. "

However, the researchers have some ideas: NGC1052-DF2 is located about 65 million light-years away in a cluster of galaxies dominated by the giant elliptical galaxy NGC 1052. Galaxy formation is turbulent and fierce, and van Dokkum points to it suggested that the growth of the still young massive galaxy could be possible billions of years ago played a role in NGC1052-DF2s lack of dark matter.

Another idea is that a cataclysmic event takes place within the weird galaxy, such as the birth of Myriads of massive stars that displaced all gas and dark matter and stopped star formation 19659004] However, these possibilities are speculative and do not explain all the properties of the observed galaxy,

The team continues the search for galaxies with dark matter Hubble images of 23 other diffuse galaxies, three of which seem to be similar to NGC105 2-DF2, which van Dokkum wants to follow in the coming months at the Keck Observatory.

"Every galaxy we know before has dark matter and they all fall into familiar categories like spiral or elliptical galaxies," van Dokkum said. "But what would you get if there were no dark matter at all? Maybe you would get that."


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