After a two years analysis on the emission spectra from a 2016 X-ray transient outburst in the black hole system U4 1630-47, obtained by three different independent space missions; Chandra/HEG, AstroSat and MAXI, the leader of the project Dr. Mayukh Pahari and collaborators could determine the spinning and mass of the BH. The estimated spinning rate is 92-95% the speed of light, with a mass of 5-10 M (million solar masses).
Fig 1 below shows the initial signals detected by the MAXI missions. These spectra are further analyzed, decomposed and fitted in order to obtain the final results published here.
Fig.1: 2016 X-ray outburst of 4U 1630–47 as observed by MAXI and Swift/BAT.
With the independent modeling of the broadband data spectra obtained by the three missions, and using the Markov chain Monte Carlo simulations on fitted spectral parameters, they find a range of the black hole spin parameter depicted in Fig. 2, amounting to 0.88–0.96 within a 3σ deviation, which indicates the presence of a rapidly spinning black hole in 4U 1630–47.
Figure 2: spin parameter for three different joint spectral fits.
This is the fifth occasion that a spinning black hole has been so firmly characterized, and the reason for such a few numbers of cases compared to the number of BH detected so far, relies on the fact that spinning black holes are very difficult to detect, as Dr. Pahari explains below.
Detecting signatures that allow us to measure spin is extremely difficult. The signature is embedded in the spectral information which is very specific to the rate at which matter falls into the black hole. The spectra, however, are often very complex mostly due to the radiation from the environment around the black hole.
Among the interesting features that the emission spectra reveals, one of most important one is the chemical elements surrounding the BH. For instance, the Chandra/HEG (High Energy Grating) spectrum shows two strong absorption lines at 6.705 keV and 6.974 keV (see Fig 3), which are produced by the element iron (Fe) in different oxidation states (Fe XXV and Fe XXVI) in a low-velocity ionized disk wind. The corresponding outflow velocity is determined to be 366±56 km/s.
Fig. 3: Absorption lines from Chandra grating spectra, showing two strong absorption lines visible at ∼6.7 and ∼6.97 keV, which are due to the ionized Fe XXV and Fe XXVI absorption features, fitted with Gaussian absorption profiles.
In view of the model proposed by Haramein, spin is at the origin of energy and mass, through the vorticial nature or torque inherent to the structure of space-time – or vacuum – itself (see here). For this reason, everything in the universe is spinning, from sub atomic particles, to planets, galaxies and beyond. The fact that all BH are spinning is difficult to realize due to the difficulties measuring the effect
Illustration credit: CXC/M. Weiss and Figures taken from original IOP article.
AstroSat and Chandra View of the High Soft State of 4U 1630–47 (4U 1630–472): Evidence of the Disk Wind and a Rapidly Spinning Black Hole