Nowadays, scientists have the ability to observe the universe across many wavelengths, including those that cannot be seen by unaided human eyes – such as infrared and gamma rays. However, there is still some “blind spots” for the astronomers in the electromagnetic spectrum, such as the high energy X-rays region.
In order to clarify our view of these cosmic X-rays, NASA has just launched the Nuclear Spectroscopic Telescope Array (NuSTAR), a sci-fi looking space observatory that will allow us to better understand the physics and chemistry behind the most extreme objects in the universe.
Artist's impression of NuSTAR on orbit. (credits: NASA/JPL-Caltech)
NuSTAR is going to observe the same kind of X-rays used in medicine – when the doctors need to take a look at our bones – and in airports – to see what’s inside our luggage. Although we have spacecraft able to take X-ray images, like NASA’s Chandra and ESA’s XMM-Newton, these facilities aren’t able to get sharp images of this energetic form of light.
Surveying the Extreme Universe
The NuSTAR’s primary mission – projected to last for at least two years – is intended to provide a detailed survey of both stellar and supermassive black holes. Although being known as objects capable of swallowing pretty much everything nearby – even light – the region around the black holes – called the accretion disk - emits vast amounts of X-ray radiation, produced by the friction between the pieces of debris orbiting the black hole. NuSTAR is equipped to detect these radiation bursts and locate black holes that would be otherwise invisible.
It’s also going to analyse the young-supernovae remnants, more specifically, the radioactive nuclei produced by the exploding stars. These nuclei are the key to understanding the conditions in which each explosions occurred, the nuclear ignition, structure and dynamics of the explosion, giving us clues as to how exactly the elements are formed in the hidden core of a star.
The brightest objects visible to NuSTAR are the jets emitted by supermassive black holes – that can be found in the core of most galaxies – in a specific kind of galaxy known as a blazar. These are a form of active galaxy that produce jets composed of particles travelling in very high speeds that happen to be pointing towards the Earth – therefore we see them much brighter than we would otherwise. By observing the variation of the light intensity of these beams, we’ll be able to figure out how the black hole’s accretion disk looks like, as well as the physical structure and composition of the jets.
And that’s not all: the probe will also peer at the Solar corona, the outer atmosphere of the Sun. This region is known for its extreme temperatures – as a matter of fact, even hotter than the Sun’s surface. By studying the corona, we can get a close-up look at the particle acceleration processes similar to those that take place in objects like supernova remnants and black hole jets.
This image comparison demonstrates NuSTAR's improved ability to focus high-energy X-ray light into sharp images. The image on the left, taken by ESA's INTEGRAL satellite, shows how we see these X-rays today. The image on the right is a simulation of what NuSTAR will see at comparable wavelengths. (Credits: ESA/NASA/JPL-Caltech)
Looking Further than Ever
What makes NuSTAR able to archive all these goals is its ingenious focusing mechanism: a pair of Wolter-I mirrors pointing at the same patch of sky. Moreover, in order to improve its reflection capacity, these mirrors are coated with structures known as “depth-graded layers”, made of a mix of low and high density materials.
The unprecedented sensibility of NuSTAR – along with the data from the other observatories – will allow us to study the universe as never before, from the surface of the Sun to the galaxies at the other edge of the universe, going through the most extreme objects known by humankind.
NuSTAR has successfully reached orbit and is preparing for the commencement of its observations.