VOLCANICALLY ACTIVE EXO-MOON
University of Bern
Jupiter's moon Io is the most volcanically active body in our solar system. Today, there are indications that an active moon outside our solar system, an exo-Io, could be hidden at the exoplanet system WASP-49b. It would be a dangerous volcanic world with a molten surface of lava, a lunar version of close-in Super Earths like 55 Cancri-e. Astronomers have not yet discovered a rocky moon beyond our solar system and it is on the basis of circumstantial evidence that researchers conclude that the exo-Io exists: sodium gas was detected at the WASP 49-b at an anomalously high altitude. The neutral sodium gas is so far away from the planet that it is unlikely to be emitted solely by a planetary wind. Observations of Jupiter and Io in our solar system, by the international team, along with mass-loss calculations, show that an exo-Io could be a very plausible source of sodium at WASP 49-b. Already in 2006, astronomers had shown that large amounts of sodium at an exoplanet could point to a hidden moon or ring of material, and ten years ago, researchers at Virginia calculated that such a compact system of three bodies: star, close-in giant planet and moon, can be stable over billions of years. The energy released by the tides to the planet and its moon keeps the moon's orbit stable, simultaneously heating it up and making it volcanically active. In their work, the researchers were able to show that a small rocky moon can eject more sodium and potassium into space through such extreme vulcanism than a large gas planet, especially at high altitudes.
The researchers compared their calculations with those observations and found five candidate systems where a hidden exomoon can survive against destructive thermal evaporation. For WASP 49-b the observed data can be best explained by the existence of an exo-Io. However, there are other options. For example, the exoplanet could be surrounded by a ring of ionized gas, or non-thermal processes. The researchers are therefore relying on further observations with ground-based and space-based instruments. While the current wave of research is going towards habitability and biosignatures, this signature is a signature of destruction. A few of these worlds could be destroyed in a few billion years owing to the extreme mass loss.
WATER DETECTED ON EXOPLANET
Université de Montréal
Ever since the discovery of the first exoplanet in the 1990s, astronomers have made steady progress towards finding and probing planets located in the habitable zone of their stars, where conditions can lead to the formation of liquid water and the proliferation of life. Results from the Kepler satellite mission, which discovered nearly 2/3 of all known exoplanets to date, indicate that 5 to 20% of Earths and super-Earths are located in the habitable zone of their stars. However, despite this abundance, probing the conditions and atmospheric properties on any of these habitable zone planets is extremely difficult and has remained elusive... until now.
A new study by the Institute for Research on Exoplanets at the Université de Montréal reports the detection of water vapour and perhaps even liquid water clouds in the atmosphere of the planet K2-18b. This exoplanet is about nine times more massive than our Earth and is found in the habitable zone of the star it orbits. This M-type star is smaller and cooler than our Sun, but due to K2-18b's close proximity to its star, the planet receives almost the same total amount of energy from its star as our Earth receives from the Sun.
The similarities between the exoplanet K2-18b and the Earth suggest to astronomers that the exoplanet may potentially have a water cycle possibly allowing water to condense into clouds and liquid water rain to fall. This detection was made possible by combining eight transit observations -- the moment when an exoplanet passes in front of its star -- taken by the Hubble Space Telescope. The Université de Montréal is no stranger to the K2-18 system located 111 light years away. The existence of K2-18b was first confirmed using data from the
Spitzer Space Telescope. Scientists currently believe that the thick gaseous envelope of K2-18b likely prevents life as we know it from existing on the planet's surface. However, the study shows that even these planets of relatively low mass which are therefore more difficult to study can be explored using astronomical instruments developed in recent years. By studying these planets which are in the habitable zone of their star and have the right conditions for liquid water, astronomers are one step closer to directly detecting signs of life beyond our Solar System.
GIANT MAGNETIC 'BRIDGE' BETWEEN GALAXIES
Science Alert
For the first time, scientists have detected evidence of a magnetic field that is associated with the vast intergalactic 'bridge' that links our two nearest galactic neighbours. Known as the Magellanic Bridge, the bridge is a huge stream of neutral gas that stretches some 75,000 light-years between the Large and Small Magellanic Clouds (LMC and SMC). Although researchers had predicted it was there, this is the first observation of its magnetic field, and it could help us understand how these vast bridges came to be. Our closest galactic neighbours, the LMC and SMC) are 160,000 and 200,000 light-years away respectively, and are visible in the southern night sky. Researchers have long known about the Magellanic Bridge that exists between those neighbours, a path with a few known stars inside it. But until now, very little was known about the magnetic field associated with the bridge. The team has now shown that the newly detected magnetic field is one millionth the strength of Earth's own protective magnetic shield -- and it could provide some insight into how it formed.
Two of the leading options are that the magnetic field was generated from within the bridge after the structure formed, or it may have been 'ripped' from the dwarf galaxies thought to have merged and formed the bridge in the first place. If a bridge between the stars sounds a little sci-fi to you, keep in mind that most of space is filled with different magnetic fields. Not only are entire galaxies magnetic, but the faint delicate threads joining galaxies are magnetic, too. Everywhere we look in the sky, we find magnetism. The reason we've struggled to study this structure in the past is the fact that these types of cosmic magnetic fields can only be observed indirectly through their effect on other structures in space. In this case, radio signals from hundreds of very distant galaxies were used to pick up the magnetic field associated with the Magellanic Bridge. Radio signals can be thought of like waves on the surface of a pond, in that they vibrate along a particular plane in space. When these radio signals pass through a magnetic field, that plane is rotated, and it allows astronomers to measure the strength and polarity (direction) of the field. The radio emission from the distant galaxies served as background 'flashlights' that shine through the Bridge. Its magnetic field then changes the polarization of the radio signal. How the polarized light is changed tells us about the intervening magnetic field. Now that scientists have been able to detect the field, they have a chance to work out not only how it formed, but the impact it has had on the LMC and SMC.
ARE BLACK HOLES MADE OF DARK ENERGY?
University of Hawaii at Manoa
Researchers have identified and corrected a subtle error that was made when applying Einstein's equations to model the growth of the Universe. Physicists usually assume that a cosmologically large system, such as the Universe, is insensitive to details of the small systems contained within it. Now scientists have shown that that assumption can fail for the compact objects that remain after the collapse and explosion of very large stars. For 80 years, astronomers assumed that the Universe, in broad strokes, was not affected by the particular details of any small region. It is now clear that general relativity can observably connect collapsed stars -- regions the size of a terrestrial town -- to the behaviour of the Universe as a whole, billions of times larger. The researchers demonstrated that the growth rate of the Universe can become sensitive to the averaged contribution of such compact objects. Likewise, the objects themselves can become linked to the growth of the Universe, gaining or losing energy depending on the objects' compositions. This result is significant since it reveals unexpected connections between cosmological and compact object physics, which in turn leads to many new observational predictions. One consequence of this study is that the growth rate of the Universe provides information about what happens to stars at the end of their lives. Astronomers typically assume that large stars form black holes when they die, but this is not the only possible outcome. In 1966, Erast Gliner, a young physicist at the Ioffe Physico-Technical Institute in Leningrad, proposed an alternative hypothesis, that very large stars should collapse into what could now be called Generic Objects of Dark Energy (GEODEs). They appear to be black holes when viewed from the outside but, unlike black holes, they contain Dark Energy instead of a singularity.
In 1998, two independent teams of astronomers discovered that the expansion of the Universe is accelerating, consistent with the presence of a uniform contribution of Dark Energy. It was not recognized, however, that GEODEs could contribute in that way. With the corrected formalism, it has been shown that if a fraction of the oldest stars collapsed into GEODEs, instead of black holes, their averaged contribution today would naturally produce the required uniform Dark Energy. The results of this study also apply to the colliding double-star systems observable through gravitational waves by the LIGO-Virgo collaboration. In 2016, LIGO announced the first observation of what appeared to be a colliding double-black-hole system. Such systems were expected to exist, but the pair of objects was unexpectedly massive -- roughly 5 times larger than the black-hole masses predicted in computer simulations. Using the corrected formalism, astronomers considered whether LIGO-Virgo is observing double GEODE collisions, instead of double black-hole collisions. They found that GEODEs grow together with the Universe during the time leading up to such collisions. When the collisions occur, the resulting GEODE masses become 4 to 8 times larger, in rough agreement with the LIGO-Virgo observations. The team was careful to separate the theoretical result from observational support of a GEODE scenario, emphasizing that "black holes certainly aren't dead". What has been shown is that if GEODEs do exist, then they can easily give rise to observed phenomena that presently lack convincing explanations. We anticipate numerous other observational consequences of a GEODE scenario, including many ways to exclude it. We have barely begun to scratch the surface.
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