New images from the SPHERE instrument on ESO’s Very Large Telescope are revealing the dusty discs surrounding nearby young stars in greater detail than previously achieved. They show a bizarre variety of shapes, sizes and structures, including the likely effects of planets still in the process of forming. [Larger images]New images from the SPHERE instrument on ESO’s Very Large Telescope are revealing the dusty discs surrounding nearby young stars in greater detail than previously achieved. They show a bizarre variety of shapes, sizes and structures, including the likely effects of planets still in the process of forming.
The SPHERE instrument on ESO’s Very Large Telescope (VLT) in Chile allows astronomers to suppress the brilliant light of nearby stars in order to obtain a better view of the regions surrounding them. This collection of new SPHERE images is just a sample of the wide variety of dusty discs being found around young stars.
These discs are wildly different in size and shape — some contain bright rings, some dark rings, and some even resemble hamburgers. They also differ dramatically in appearance depending on their orientation in the sky — from circular face-on discs to narrow discs seen almost edge-on.
SPHERE’s primary task is to discover and study giant exoplanets orbiting nearby stars using direct imaging. But the instrument is also one of the best tools in existence to obtain images of the discs around young stars — regions where planets may be forming. Studying such discs is critical to investigating the link between disc properties and the formation and presence of planets.
This spectacular image from the SPHERE instrument on ESO’s Very Large Telescope shows the dusty disc around the young star IM Lupi in finer detail than ever before. [Larger versions]Many of the young stars shown here come from a new study of T Tauri stars, a class of stars that are very young (less than 10 million years old) and vary in brightness. The discs around these stars contain gas, dust, and planetesimals — the building blocks of planets and the progenitors of planetary systems.
These images also show what our own Solar System may have looked like in the early stages of its formation, more than four billion years ago.
Most of the images presented were obtained as part of the DARTTS-S (Discs ARound T Tauri Stars with SPHERE) survey. The distances of the targets ranged from 230 to 550 light-years away from Earth. For comparison, the Milky Way is roughly 100 000 light-years across, so these stars are, relatively speaking, very close to Earth. But even at this distance, it is very challenging to obtain good images of the faint reflected light from discs, since they are outshone by the dazzling light of their parent stars.
This SPHERE observation is the discovery of an edge-on disc around the star GSC 07396-00759, which is a member of a multiple star system included in the DARTTS-S sample. Oddly, this new disc appears to be more evolved than the gas-rich disc around the T Tauri star in the same system, although they are the same age. The disc extends from the lower-left to the upper-right and the central grey region shows where the star was masked out. [Larger images]Another new SPHERE observation is the discovery of an edge-on disc around the star GSC 07396-00759, found by the SHINE (SpHere INfrared survey for Exoplanets) survey. This red star is a member of a multiple star system also included in the DARTTS-S sample but, oddly, this new disc appears to be more evolved than the gas-rich disc around the T Tauri star in the same system, although they are the same age. This puzzling difference in the evolutionary timescales of discs around two stars of the same age is another reason why astronomers are keen to find out more about discs and their characteristics.
The new results from SPHERE, along with data from other telescopes such as ALMA, are revolutionising astronomers’ understanding of the environments around young stars and the complex mechanisms of planetary formation.
This image composite shows the discovery of the most distant known star using the NASA/ESA Hubble Space Telescope. The image to the left shows a part of the the deep-field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme gathered in 2014. The square indicates the position where the star appeared in May 2016 — its image magnified by gravitational microlensing. This part of the image also shows the four images of the Refsdal supernova, arranged in an Einstein cross. The upper right image pinpoints the position of the star, observed in 2011. The lower right image shows where the star was undergoing the microlensing event in late May 2016. [Larger image]Astronomers using the NASA/ESA Hubble Space Telescope have found the most distant star ever discovered. The hot blue star existed only 4.4 billion years after the Big Bang. This discovery provides new insight into the formation and evolution of stars in the early Universe, the constituents of galaxy clusters and also on the nature of dark matter.
The international team, led by Patrick Kelly (University of Minnesota, USA), Jose Diego (Instituto de Física de Cantabria, Spain) and Steven Rodney (University of South Carolina, USA), discovered the distant star in the galaxy cluster MACS J1149-2223 in April 2016.
This animation shows the effect of strong gravitational lensing, which can also be seen in the galaxy MACS J1149-2223. The mass of the galaxy cluster bends and magnifies the light of more distant objects in the background, making them appear brighter and hence allows telescopes to see them; it also leads to multiple images of the same object. This way Hubble detected the most distant star know to date, called LS1.
The observations with Hubble were actually performed in order to detect and follow the latest appearance of the gravitationally lensed supernova explosion nicknamed “Refsdal” (heic1525)[1], when an unexpected point source brightened in the same galaxy that hosted the supernova.
“Like the Refsdal supernova explosion the light of this distant star got magnified, making it visible for Hubble,” says Patrick Kelly. “This star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”
The observed light from the newly discovered star, called Lensed Star 1 (LS1) was emitted when the Universe was only about 30 percent of its current age — about 4.4 billion years after the Big Bang. The detection of the star through Hubble was only possible because the light from the star was magnified 2000 times.
“The star became bright enough to be visible for Hubble thanks to a process called gravitational lensing,”
explains Jose Diego. The light from LS1 was magnified not only by the huge total mass of the galaxy cluster, but also by another compact object of about three times the mass of the Sun within the galaxy cluster itself; an effect known as gravitational microlensing[2].
“The discovery of LS1 allows us to gather new insights into the constituents of the galaxy cluster. We know that the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole,”
explains Steven Rodney. LS1 therefore allows astronomers to study neutron stars and black holes, which are otherwise invisible and they can estimate how many of these dark objects exist within this galaxy cluster.
This image shows the the huge galaxy cluster MACS J1149.5+223, whose light has taken over 5 billion years to reach us. Highlighted is the position where the star LS1 appeared — its image magnified by a factor 2000 by gravitational microlensing. The galaxy in which the star is located can be seen three times on the sky — multiplied by strong gravitational lensing. [ Larger image]As galaxy clusters are among the largest and most massive structures in the Universe, learning about their constituents also increases our knowledge about the composition of the Universe overall. This includes additional information about the mysterious dark matter.
“If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1. Our observations do not favour the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun”,
highlights Kelly.
This video shows the galaxy cluster MACS J1149.5+223. Thanks to a lucky alignment between the cluster, a dense object within it and a distant star, the image of the distant star was magnified by a factor of 2000, making it visible by the NASA/ESA Hubble Space Telescope. Like the galaxy in which the star is located, the star is actually visible several times. However, the light from the second image of the star was redirected by another massive object in the cluster and only became visible when this object moved out of the line of sight. The video shows the position of the two images of the star within the cluster.
After the discovery the researchers used Hubble again to measure a spectrum of LS1. Based on their analysis, the astronomers think that LS1 is a B-type supergiant star. These stars are extremely luminous and blue in colour, with a surface temperature between 11 000 and 14 000 degrees Celsius; making them more than twice as hot as the Sun.
But this was not the end of the story. Observations made in October 2016 suddenly showed a second image of the star.
“We were actually surprised to not have seen this second image in earlier observations, as also the galaxy the star is located in can be seen twice,” comments Diego. “We assume that the light from the second image has been deflected by another moving massive object for a long time — basically hiding the image from us. And only when the massive object moved out of the line of sight the second image of the star became visible.”
This second image and the blocking object add another piece of the puzzle to reveal the makeup of galaxy clusters.
With more research and the arrival of new, more powerful telescopes like the NASA/ESA/CSA James Webb Space Telescope, the astronomers suggest that with microlensing, it will be possible to study the evolution of the earliest stars in the Universe in greater detail than ever expected.
This image shows the huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us. The huge mass of the cluster is bending the light from more distant objects. The light from these objects has been magnified and distorted due to gravitational lensing. The same effect is creating multiple images of the same distant objects. [ Larger image]Notes
[1] Observations of this supernova, nicknamed Refsdal in honour of the Norwegian astronomer Sjur Refsdal, were made as part of Hubble’s Frontier Fields project.
[2] Gravitational lensing magnifies the light from fainter, background objects, allowing Hubble to see objects it would otherwise not be able to detect. The process was first predicted by Albert Einstein and is now used to find some of the most distant objects in the Universe. Usually the lensing object is a galaxy or a galaxy cluster, but in some cases it can also be a star or even a planet. When it involves these smaller objects the process is called microlensing.
This short clip shows an animation of the B-type supergiant star LS1 which was discovered with the help of gravitational lensing. These stars are extremely luminous and blue in colour, with a surface temperature between 11 000 and 14 000 degrees Celsius; making them more than twice as hot as the Sun. Credit: ESA/Hubble, M. Kornmesser
An international team of researchers using the NASA/ESA Hubble Space Telescope and several other observatories have, for the first time, uncovered a galaxy in our cosmic neighborhood that is missing most — if not all — of its dark matter. This discovery of the galaxy NGC 1052-DF2 challenges currently-accepted theories of and galaxy formation and provides new insights into the nature of dark matter. The results are published in Nature.
NGC 1052-DF2 resides about 65 million light-years away in the NGC 1052 Group, which is dominated by a massive elliptical galaxy called NGC 1052. This large, fuzzy-looking galaxy is so diffuse that astronomers can clearly see distant galaxies behind it. This ghostly galaxy is not well-formed. It does not look like a typical spiral galaxy, but it does not look like an elliptical galaxy either. Based on the colours of its globular clusters, the galaxy is about 10 billion years old. However, even the globular clusters are strange: they are twice as large as typical groups of stars. All of these oddities pale in comparison to the weirdest aspect of this galaxy: NGC 1052-DF2 is missing most, if not all, of its dark matter. The galaxy contains only a tiny fraction of dark matter that astronomers would expect for a galaxy this size. But how it formed is a complete mystery. Hubble took this image on 16 November 2017 using its Advanced Camera for Surveys.
Astronomers using Hubble and several ground-based observatories have found a unique astronomical object: a galaxy that appears to contain almost no dark matter [1]. Hubble helped to accurately confirm the distance of NGC 1052-DF2 to be 65 million light-years and determined its size and brightness. Based on these data the team discovered that NGC 1052-DF2 larger than the Milky Way, but contains about 250 times fewer stars, leading it to be classified as an ultra diffuse galaxy.
“I spent an hour just staring at this image,” lead researcher Pieter van Dokkum of Yale University says as he recalls first seeing the Hubble image of NGC 1052-DF2. “This thing is astonishing: a gigantic blob so sparse that you see the galaxies behind it. It is literally a see-through galaxy.”
Further measurements of the dynamical properties of ten globular clusters orbiting the galaxy allowed the team to infer an independent value of the galaxies mass. This mass is comparable to the mass of the stars in the galaxy, leading to the conclusion that NGC 1052-DF2 contains at least 400 times less dark matter than astronomers predict for a galaxy of its mass, and possibly none at all [2]. This discovery is unpredicted by current theories on the distribution of dark matter and its influence on galaxy formation.
“Dark matter is conventionally believed to be an integral part of all galaxies — the glue that holds them together and the underlying scaffolding upon which they are built,” explains co-author Allison Merritt from Yale University and the Max Planck Institute for Astronomy, Germany. And van Dokkum adds: “This invisible, mysterious substance is by far the most dominant aspect of any galaxy. Finding a galaxy without any is completely unexpected; it challenges standard ideas of how galaxies work.”
Merritt remarks:
“There is no theory that predicts these types of galaxies — how you actually go about forming one of these things is completely unknown.”
Although counterintuitive, the existence of a galaxy without dark matter negates theories that try to explain the Universe without dark matter being a part of it [3]: The discovery of NGC 1052-DF2 demonstrates that dark matter is somehow separable from galaxies. This is only expected if dark matter is bound to ordinary matter through nothing but gravity.
This video zooms in from a view of the night sky, through the constellation of Cetus (the Whale), to end on the NASA/ESA Hubble Space Telescope observations of the ultra diffuse galaxy NGC 1052-DF2. This is the first galaxy to be found to not have dark matter. Credit: ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org). Music: Astral Electronic
Meanwhile, the researchers already have some ideas about how to explain the missing dark matter in NGC 1052-DF2. Did a cataclysmic event such as the birth of a multitude of massive stars sweep out all the gas and dark matter? Or did the growth of the nearby massive elliptical galaxy NGC 1052 billions of years ago play a role in NGC 1052-DF2’s dark matter deficiency?
These ideas, however, still do not explain how this galaxy formed. To find an explanation, the team is already hunting for more dark-matter deficient galaxies as they analyse Hubble images of 23 ultra-diffuse galaxies — three of which appear to be similar to NGC 1052-DF2.
This image shows the sky around the ultra diffuse galaxy NGC 1052-DF2. It was created from images forming part of the Digitized Sky Survey 2. NGC 1052-DF2 is basically invisible in this image. It is located to the southwest of the bright elliptical galaxy NGC 1052, which is dominating the field of view, and east of the bright red star HD 16873.
Notes
[1] The galaxy was identified with the Dragonfly Telephoto Array (DFA) and also observed by the Sloan Digital Sky Survey (SDSS). As well as the NASA/ESA Hubble Space Telescope, the Gemini Observatory and the Keck Observatory were used to study the object in more detail.
[2] Since 1884 astronomers have invoked dark matter to explain why galaxies do not fly apart, given the speed at which the stars within galaxies move. From Kepler’s Second Law it is expected that the rotation velocities of stars will decrease with distance from the centre of a galaxy. This is not observed.
[3] The MOND theory — Modified Newtonian Dynamics — suggests that the phenomena usually attributed to dark matter can be explained by modifying the laws of gravity. The result of this would be that a signature usually attributed to dark matter should always be detected, and is an unavoidable consequence of the presence of ordinary matter.
Pink Floyd notwithstanding, there is no “Dark side of the Moon” any more than there is a dark side of the earth. The Moon rotates just like earth does, continually changing which half of the sphere is in sunlight and which half in darkness. Our celestial companion keeps one face turned towards us as it orbits around the earth, which means it takes a month rather than 24 hours to make its full 360 degree rotation. Here is a compilation of images from the Lunar Reconnaissance Orbiter (LRO) showing how the Moon would appear if you could sit fixed on a line between the Moon and the sun for a month: APOD: 2018 March 18 – Rotating Moon from LRO
Explanation: No one, presently, sees the Moon rotate like this. That’s because the Earth’s moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has been composed. The above time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Currently, over 20 new missions to the Moon are under active development from four different countries, most of which have expected launch dates either this year or next.
