The Week in Space and Physics: An Explosion Like No Other
On the biggest explosion ever seen, JUICE and Jupiter, TRAPPIST 1B and an ultra-massive black hole
Voyager 1 spotted it first. From its viewpoint, perched twenty billion miles from Earth, the wave of energy sweeping towards the Solar System showed up as a burst of activity in its particle detectors. Hours later, as the wave buffeted Mars, rovers and satellites scattered across the planet registered its arrival.
On Earth, spacecraft and telescopes were briefly blinded by its power, leaving us somewhat unsure of how much energy was surging past. At blame, astronomers soon realised, was a Gamma Ray Burst - a type of powerful but distant cosmic explosion. Yet this one was of unusual power; measuring seventy times brighter than any seen before. Later analysis suggested it may have been the largest explosion seen by humanity since the dawn of civilization.
To put that in context, the burst emitted as much energy in a few seconds as the Sun does in ten billion years. And, even though it detonated some two billion light years away, it hit Earth with enough force to shake the atmosphere. Indeed, so intense was it that radio signals were briefly disturbed as the ionosphere swelled in response.
Astronomers soon swung into action, taking advantage of a rare chance to study a cataclysm of truly cosmic proportions. The first results of their studies were recently published in a special edition of The Astrophysical Review Letters.
One area of investigation covered the possibility of a related supernova explosion. Past gamma ray bursts have been seen coming from supernova, and are thought to sometimes originate as a massive star collapses into a black hole. Yet follow-up observations failed to find any clear evidence that a supernova occurred in this case.
That could be because the resulting black hole swallowed all the evidence a supernova would leave behind. But it could also be because the gamma ray burst came from another source: the collision of two neutron stars.
That, if true, would be no surprise. Neutron star collisions are some of the most violent events known. They release so much energy that we have even picked up gravitational waves - ripples in the fabric of space and time - coming from them.
When gamma ray bursts erupt, whether from supernova or from neutron stars, they send two narrow jets of energy shooting out into space. This helps to explain why they are so bright - we only see them when a jet happens to be pointing in our direction. In this case we seem to have been lucky, as the authors of one of the papers point out.
Analysis showed the source was both nearby - two billion light years, instead of the more usual ten billion - and pointed right at us, shining a spotlight of energy on the Milky Way. Such events are extraordinarily rare, they concluded. Nothing like it may have happened since the dawn of civilization ten thousand years ago. Another is unlikely to come for at least that long.
JUICE Sets off for Jupiter
The European Space Agency succeeded in launching its JUICE spacecraft towards Jupiter last Friday. JUICE, which stands for “Jupiter Icy Moons Explorer”, will explore Jupiter and three of its moons: Callisto, Europa and Ganymede.
Onboard are a set of ten instruments, including cameras, spectrographs, radars and magnetometers. Some of these, ESA notes, are the most powerful such devices ever sent to the outer solar system. They should give researchers a better view of Jupiter and its moons than ever before.
Though the spacecraft is not designed to spot signs of life, one of its key goals is to assess the habitability of Jupiter’s moons. As hopes of finding life on Mars have faded, attention has turned to the large moons found around Jupiter and Saturn. Many of these seem to host large oceans, and scientists have wondered if living creatures may dwell within them.
Yet JUICE will also shed new light on other details of the Jovian system. Researchers hope it will tell us more about Jupiter’s atmosphere, including its famous Great Red Spot. They expect it to reveal details of the planet’s powerful magnetic field, and to explore the way it interacts with Jupiter’s moons, some of which have their own magnetic fields.
The probe will pay special attention to Ganymede, the largest moon in the Solar System. Indeed, JUICE will spend several months in orbit around Ganymede, studying the moon’s surface and magnetic fields. Past observations of Ganymede, taken with the Hubble Space Telescope, show that a vast ocean is buried deep under Ganymede’s surface. Life, some speculate, could exist there.
Oddly, though, JUICE will pay less attention to Europa, long thought the most promising candidate for life in the outer solar system. Instead that moon will receive a dedicated explorer in the form of the Europa Clipper, a NASA probe planned for launch in October 2024. Both the Europa Clipper and JUICE will explore the Jovian system throughout the first half of the next decade. JUICE, following last week’s launch, is not expected to arrive until 2031.
TRAPPIST 1B Looks Like a Dead World
Compared to the hundreds of solar systems now known to be scattered across the galaxy, ours is something of an outlier. Most, indeed, appear rather more chaotic: featuring giant planets orbiting far closer than Mercury, or rocky planets flung far into cold and remote orbits.
That makes the TRAPPIST-1 system, a set of seven small, rocky planets around a cool dwarf star look all the more intriguing. Unlike many other solar systems, these planets appear to be following steady orbits around their sun. Many of them seem to be placed in the right spots for liquid water to exist on their surfaces.
TRAPPIST-1 was, therefore, one of the most eagerly anticipated targets of the James Webb Space Telescope. It promised to reveal more data about these worlds, letting us probe their atmospheres and even look for signs of alien biology. So great was the potential, indeed, that TRAPPIST-1 was one of the first objects to be surveyed by the telescope.
The first results of that survey are now in, but, sadly, they are not encouraging. Measurements of TRAPPIST-1b, the innermost world of that solar system, show a boiling hot planet. The James Webb measured temperatures reaching hundreds of degrees. Climate models of TRAPPIST-1b therefore suggest the planet has no atmosphere at all. It seems, in all likelihood, to be something much more like Mercury than Earth.
Still, there are six other planets in the TRAPPIST system. The James Webb has already collected data on each of them. If any are habitable, perhaps with a thick Earth-like atmosphere, we should soon find out.
An Ultra-Massive Black Hole
Astronomers recently used a new technique to discover a vast black hole located in a distant galaxy. The black hole is so enormous that it seems to be one of the largest ever spotted, and may even lie close to the theoretical limit on how big black holes can grow.
Large black holes distort the space around them. This effect means they sometimes act as “lenses”, amplifying light coming from more distant objects behind them. In this case the black hole amplified and distorted our view of another galaxy, stretching it out into a long arc.
The exact pattern of distortion depends not only on the position of the black hole, but also its mass. By running simulations of the patterns different black holes would create, researchers were able to find one that closely fit the observations. This, they say, suggests the black hole is exceptionally large - weighing in at over thirty billion times the mass of the Sun.