# Radio astronomy of black hole

1. Jul 31, 2012

### isha89

Is it feasible to perform space VLBI at 230 GHz? Also how does one detect the radio jets at 230 GHz?

2. Jul 31, 2012

### SpiffyKavu

I don't know if it has been done before, but take a look at the event horizon telescope. It is designed to be a mm-VLBI instrument.

Why are you interested in 230 GHz? It happens to be among the strongest transition lines for the carbon monoxide molecule (2nd most abundant molecule after H$_2$). Either way, 230 Ghz corresponds to a wavelength of 1.3mm, which means it is easily accessible to the CARMA, which is an array of millimeter to centimeter telescopes. It uses up to 23 dishes which can be moved around depending on the observations.

At this frequency, we are stepping out of the radio regime. Black hole jets emit most of the synchrotron radiation at much lower wavelengths. In general, though, we can map out a jet by taking measurements of the intensity of the light at different locations on the sky. One can also take measurements of different frequencies at a point on the sky. Most radio/mm observations do both.

3. Aug 1, 2012

### isha89

Well, the resolution of millimeter and submillimeter wavelength VLBI is well matched to the scale of inner disk physics. Base- lines from Hawaii or Western Europe to Chile provide fringe spacings as small as 30 μas (3 RS) at 230 GHz and 20 μas at 345 GHz. Millimeter VLBI thus has the potential to de- tect signatures of hot spot and jet models proposed to explain the rapid variability of Sgr A* as well as strong general relativistic effects, such as the black hole silhouette or shadow. Also the man made noise will also be eliminated if we use a space based technique.

What I'm confused about now is how to calculate the gain of the radio antenna at 230GHz. Because the gain requires the power radiated by the source. I only managed to obtain a value for bolometric luminosity which is 10^36 erg/s. But can this be used to calculate gain?
How do I calculate brightness temperature ?? I do not know the value of blackbody temperature T.
T = Bn(T)c2/2kn2