Scientists have discovered a new way to measure distances to sources of X-rays in space. The discovery is based on the echoes of the X-rays, which were radiated from one of our galaxy’s oddest supernovae. Scientists say that Circinus X-1 is a freak of the Milky Way and now believe they have founded an application for the rays it gives off – thus yielding a new “measuring stick” for astronomers.
Circinus X-1 is located in the plane of the Milky Way. It can be described as a glowing husk of a binary star system that exploded a mere 2,500 years ago. Circinus X-1 consists of a nebula and a neutron star, the extremely dense collapsed core of the exploded star, still in the orbital embrace of its companion star. This system emits X-rays, because material from smaller companion star moves in a spiral form into the bigger and much denser neutron star, where it is heated to extremely high temperatures.
Circinus X-1 faced changes in the late 2013, when the neutron star had a massive outburst for about two months, during which it became one of the brightest sources of X-rays in the sky. After the outburst it turned dark again. This outburst was monitored by a detector aboard the International Space Station. Professor Sebastian Heinz from the University of Wisconsin-Madison and his team of scientists started follow-up observations, using the space-based Chandra and XMM-Newton telescopes, and discovered four bright rings of X-rays around the neutron star at the heart of Circinus X-1. These rings look like ripples in the water of the pond.
Scientists knew that these rings are light echoes from the X-ray burst. Professor Heinz says that each of these rings indicates a dense cloud of dust between us and the supernova remnant. As the X-rays from the outburst meet grains of dust in interstellar space they can be deflected. If the cloud of dust is dense enough, X-rays can get scattered away from their original trajectory, putting them on a triangular path. This is the phenomenon that gave scientists the idea about the measuring stick.
Team of scientists figured out that the geometry of the rings and a time delay between deflected and undeflected X-rays could give the opportunity for scientists to calculate the distance to Circinus X-1. Previously this measurement was not possible, because the supernova is hidden in the dust of the Milky Way. Professor Heinz explained that now scientists can “use the geometry of the rings and the time delay to do X-ray tomography, because the X-rays have travelled on a triangular path rather than a straight path, they take longer to get to us than the ones that were not scattered.”
Team of astronomers then combined those measurements with observations of the dust clouds by Australia’s Mopra radio telescope to determine which dust clouds were responsible for each of the four light echoes. Using this method and data from other observations scientists were able to determine the distance to the source of X-rays accurately for the first time. Methods like this are very useful, if scientists will be able to use it on other objects as well. Measurements of distance to sources like Circinus X-1 are extremely difficult, because of a thick layer of dust that hides them in the plane of the galaxy and makes them impossible to observe with optical telescopes. However, because of creative thinking of the scientists now this cloud became a possibility rather than an obstacle and scientists have pioneered a new method to use the dust to estimate the distances to X-ray sources.
Even though it seems to be a complicated and very sophisticated way to get to know the distance to one object in the sky, it is extremely useful. It will be used to estimate distances to other objects, which cannot be observed with current telescopes, as well. And now scientists know that the distance between the Earth and one of the most bizarre objects in the Milky Way Circinus X-1 system is 30,700 light-years.