A neutron star resembles a giant atomic nucleus, with 1–2 times the Sun’s mass packed into a ball about 20 kilometres across. Its gravity is so strong that a projectile would need to be launched at about half the speed of light to escape from its surface. Extreme density, pressure, temperature, magnetism and relativistic gravity make these objects fascinating but challenging to study. Surprising observations of spin-down irregularities in one intensely magnetized neutron star, reported by Archibald et al.1 on page 591 of this issue, offer clues about exotic processes occurring deep inside these objects.
The basic structure of a neutron star is generally agreed on. It has a crust about 1 km thick, in which nuclei are arranged in a crystal lattice immersed in a ‘sea’ of electrons. Near the surface, the nuclei are plain iron, but the pressure and density increase rapidly with depth, so that the nuclei become increasingly bloated and neutron-rich. At moderate depth, neutrons ‘drip’ out of the nuclei, forming a neutral liquid between the lattice nuclei. At the base of the crust, the bloated nuclei merge. Below this lies pure nuclear fluid, more than 200 trillion times denser than liquid water.
For one sleepless week in early September 2009, Garth Illingworth and his team had the early Universe all to themselves. At NASA’s request, Illingworth, Rychard Bouwens and Pascal Oesch had just spent the previous week staring into their computer screens at the University of California, Santa Cruz, scanning through hundreds of black-and-white portraits of faint galaxies recorded in a multi-day time exposure by a newly installed infrared camera on the Hubble Space Telescope. NASA simply wanted the three astronomers to preview the images and make sure that the camera was working correctly, before the agency released the data more widely.
If all the light emitted by all galaxies in the observable universe at all wavelengths during all of cosmic history were known, it would clue astronomers about the entire history of galaxy formation and evolution, and provide insights to key aspects of the expansion history of the universe. But measuring this light — known as extragalactic background light (EBL) — is no simple task, complicated by the fact that Earth is lodged inside a bright solar system and the Milky Way, a very bright galaxy, making it enormously difficult for ground-based and space-based telescopes to reliably measure EBL. Furthermore, current galaxy surveys being used to estimate EBL could very well be missing information from faint galaxies and other sources.
A team of astronomers has come up with a solution that ingeniously overcomes the technical challenges of measuring EBL. They propose in a paper published May 24 in The Astrophysical Journal that one answer to the problem of measuring EBL lies in measuring the attenuation — or weakening — of very high-energy gamma rays from distant “blazars,” which are supermassive black holes in the centers of galaxies.
In the week I was stopped by my next door neighbour, while on my way in from work, with the starting sentence “that’s a large telescope you were using last night, is it yours?”
“It is” I replied “It’s actually one of two that I have.”
“Ah I see, my son saw you out there with it the other night, but was too shy to come over and ask for a look”
“That’s no problem at all” I said “He’s welcome to come and have a look at any time. Assuming the skies are clear over the weekend, I”ll get them both out and set up, and we can do a bit of viewing”
So, Sunday evening arrives and the skies are perfectly clear. I have a group of friends with me (who also wanted to see what was going on in the skies). I set up both of my scopes, the 8″ Skywatcher 200 and the 3″ Skywatcher 102. The 102 is computer driven and this would be the first time I had used it in such a configuration since having it.
I started the evening with a small sky orientation, using the same reference points, that I use to align the 102. Vega (located in East), Arcturus (in the South West) and then pointed out Saturn (also in the South West) and Polaris (in the North) These are the main objects that I use, when I am out, as they are most familiar to me in relation to my surroundings (i.e. my garden)
The first object of interest we looked at, was Saturn. Fairly low in the South-West, just peaking above the roof top of the adjoining houses. It was particularly clear and crisp. I had the 8″ on it, with a 25mm eyepiece and 2x Barlow, so the view of the rings was pretty spectacular. The Cassini division was clearly visible, as at the current time, the rings are tilted down towards us. Saturn was the first of the planets that I ever saw through a telescope, and I am pretty sure it is what got me hooked on astronomy. It’s always a good reliable object to view for first timers, as it has that WOW factor. (Plus, at this point the Moon hadn’t risen above the horizon)
Next we moved on to play a game that I call “Red Star, Blue Star” I use this to show that stars have different colours and how this relates to physical parameters of stars. We used Vega and Arcturus for this as the colour difference between the two. I explained that blue stars, are generally large very hot yet short lived (in star terms) and that red stars are cooler, and yet live a lot longer. This then led on to the talk about stellar distances, the light year, and how astronomy is basically time travel.
After all looking at both stars, I then used the 102 to point to a number of different star clusters (M13, M92 and M5) and had a discussion about them and what they are.
The hardest question of the night, was trying to explain what would happen if gravity between binary stars stopped. Tricky because its hard to explain to a 10 year old the answer to this question, and not go into too much detail about general relativity. However I think we managed.
Finally, around 11pm the Moon made a spectacular appearance from below the horizon. Bright vibrant orange. Attention to this then took up the rest of the night. Both the 200 and the 105 were slewed to it. The 102 using a 35mm camera projection wide angle eyepiece, and the 200 the same 25mm with 2x barlow. The craters were lovely in the orange light, and made for great viewing. There were lots of images taken using iPhones by the members of the group.
Hopefully the evening of astronomy helped inspire a new generation of amateurs, and as the year goes on, hopefully I can hold another evening, when there are different objects visible.
The Thirty Meter Telescope (TMT) – soon to be the world’s widest eye on space – has got the go-ahead for construction on the summit of Mauna Kea, Hawaii. Most of Mauna Kea is below sea level. When measured from its oceanic base, its height is 33,500 ft (10,200 m)—more than twice Mount Everest’s base-to-peak height. The sacred mountain is about one million years old –long past the most active shield stage of life hundreds of thousands of years ago–providing a stable platform for what will will be the world’s most advanced and capable ground-based optical, near-infrared, and mid-infrared observatory.
The TMT will integrate the latest innovations in precisions control, segmented mirror design, and adaptive optics. The giant eye will enable groundbreaking advances in a wide range of scientific areas, from the most distantreaches of the Universe to our own Solar System. TMT will allow astronomers to explore virtually every aspect of this picture, from inflation to exoplanets.
The resolution and sensitivity provided by its large aperture and adaptive optics systems, combined with a flexible and powerful suite of instruments, will enable astronomers to address many of the most fundamental questions ofthe coming decades.
One of the primary missions of the TMT will be the detection and analysis of life-bearing exo planets. The exoplanets that have so far been detected are gas giants like Jupiter and Neptune. They were found because their large mass noticeably perturbs the motion of the host star. Surprisingly, many are found very close to their host star. As the higher temperatures there would prevent such planets from forming, itseems that they must have migrated inward, after forming at greater distances. Most astronomers believe that smaller terrestrial planets exist, but these cannot be detected with present telescopes. The TMT will help answer such questions as are such planets common and can they survive the disruption that would result from migration of the massive planets? Do they have atmospheres like Earth?
The Hubble Space Telescope image below centers on the 100-million-solar-mass black hole at the hub of the neighboring spiral galaxy M31, or the Andromeda galaxy, the only galaxy outside the Milky Way visible to the naked eye and the only other giant galaxy in the local group. This is the sharpest visible-light image ever made of the nucleus of an external galaxy. The event horizon, the closest region around the black hole where light can still escape, is too small to be seen, but it lies near the middle of a compact cluster of blue stars at the center of the image.
The compact cluster of blue stars is surrounded by the larger “double nucleus” of M31, discovered with the Hubble Space Telescope in 1992. The double nucleus is actually an elliptical ring of old reddish stars in orbit around the black hole but more distant than the blue stars. When the stars are at the farthest point in their orbit they move slower, like cars on a crowded freeway. This gives the illusion of a second nucleus.
The blue stars surrounding the black hole are no more than 200 million years old, and therefore must have formed near the black hole in an abrupt burst of star formation. Massive blue stars are so short-lived that they would not have enough time to migrate to the black hole if they were formed elsewhere.
Astronomers are trying to understand how apparently young stars were formed so deep inside the black hole’s gravitational grip and how they survive in an extreme environment.
A strange light is shining near the centre of the Milky Way, and evidence is mounting that it is the spark of lightweight dark matter meeting a violent end. At the same time, a suite of sensitive detectors deep underground is seeing hints of similar particles.
Dark matter is thought to make up roughly 80 per cent of the matter in the universe. But aside from its gravitational tug on regular matter, the substance has proven tough to detect, and many of its fundamental properties remain unknown.
The leading theoretical candidates for dark matter are weakly interacting massive particles (WIMPs). It’s thought these particles annihilate when they meet, producing a shower of radiation, including gamma rays. Launched in 2008, NASA’s Fermi space telescope has been scanning for excess gamma rays emanating from the centre of our galaxy, where dark matter should be concentrated.
Last year scientists ruled out a possible Fermi signal at 130 gigaelectronvolts (GeV) as dark matter’s smoking gun. But there is another: In 2010, physicist Dan Hooper at Fermilab in Batavia, Illinois, and colleagues reported a possible hint from the space telescope of dark matter particles with a mass of about 10 GeV.
This is just truly remarkable! The link to this came up on my Twitter feed, and WOW what a find!
A high definition mosaic of the moon. 213 hand stitched images taken in April. If you’re not an astronaut, this might well be the next best thing!