Astronomers just switched on a device that lets them observe the Milky Way’s black hole

Astronomers working with the European Space Agency’s (ESO) Very Large Telescope (VLT) in Chile have just announced that a black hole-observing device called GRAVITY is now fully operational on all four of the VLT’s 8.2 metre (26.9 foot) Unit Telescopes – and it’s has already provided one accurate measurement.

CrazyNeutrino said:

Astronomers just switched on a device that lets them observe the Milky Way’s black hole

Astronomers working with the European Space Agency’s (ESO) Very Large Telescope (VLT) in Chile have just announced that a black hole-observing device called GRAVITY is now fully operational on all four of the VLT’s 8.2 metre (26.9 foot) Unit Telescopes – and it’s has already provided one accurate measurement.

What’s with the photo of the humidicrib at the top of the linked page?

> combine the strength of all four of the smaller Unit Telescopes that make up the VLT.

The four LARGER Unit telescopes, I assume. The VLT also has four small unit telescopes with diameters of 1.8 metres.

> “It was a fantastic moment for the whole team when the light from the star interfered for the first time – after eight years of hard work,”

LOL. We know what they mean. This is what the VLT was designed for in the first place, accurate pictures of faint stars in infra-red a long way away, so I have no idea why new equipment requiring 8 years of development time is needed.

> So far, GRAVITY has enabled scientists to examine a star called S2, which is orbiting Sagittarius A* (Sgr A*) – the hypothesised black hole at the centre of our galaxy. With the measurements they have already taken, they will hopefully find out if the star’s motion follows or deviates from those predicted by Einstein’s theory of general relativity, leading them one step closer to examining the Sgr A* itself.

ie. they’re not observing the black hole itself, only the star in orbit around it. Fingers crossed that they can also see the black hole.

mollwollfumble said:

CrazyNeutrino said:

Astronomers just switched on a device that lets them observe the Milky Way’s black hole

Astronomers working with the European Space Agency’s (ESO) Very Large Telescope (VLT) in Chile have just announced that a black hole-observing device called GRAVITY is now fully operational on all four of the VLT’s 8.2 metre (26.9 foot) Unit Telescopes – and it’s has already provided one accurate measurement.

What’s with the photo of the humidicrib at the top of the linked page?

> combine the strength of all four of the smaller Unit Telescopes that make up the VLT.

The four LARGER Unit telescopes, I assume. The VLT also has four small unit telescopes with diameters of 1.8 metres.

> “It was a fantastic moment for the whole team when the light from the star interfered for the first time – after eight years of hard work,”

LOL. We know what they mean. This is what the VLT was designed for in the first place, accurate pictures of faint stars in infra-red a long way away, so I have no idea why new equipment requiring 8 years of development time is needed.

> So far, GRAVITY has enabled scientists to examine a star called S2, which is orbiting Sagittarius A* (Sgr A*) – the hypothesised black hole at the centre of our galaxy. With the measurements they have already taken, they will hopefully find out if the star’s motion follows or deviates from those predicted by Einstein’s theory of general relativity, leading them one step closer to examining the Sgr A* itself.

ie. they’re not observing the black hole itself, only the star in orbit around it. Fingers crossed that they can also see the black hole.

GRAVITY seems to be written as an acronym?
Got the bit about the VLT with it’s four combined telescopes that view the spectrum etc.
Where does GRAVITY come in in relation to VLT?
I’d imagine you’d view a black hole as a shadow in front of light sources beyond it?

GRAVITY is the device that combines the images from all four telescope. Makes them a powerful interferometer.

ChrispenEvan said:

GRAVITY is the device that combines the images from all four telescope. Makes them a powerful interferometer.

OK, so it has nothing to do with gravity as such.

General Relativity Analysis via Vlt InTerferometrY

it will look at the BH in the centre of our galaxy.

https://www.eso.org/sci/facilities/develop/instruments/gravity.html

sciencey.

they like catchy acronyms

https://www.eso.org/sci/facilities/develop.html

ChrispenEvan said:

General Relativity Analysis via Vlt InTerferometrY

it will look at the BH in the centre of our galaxy.

https://www.eso.org/sci/facilities/develop/instruments/gravity.html

sciencey.

GRAVITY provides high precision narrowangle astrometry and phase-referenced interferometric imaging in the astronomical K-band (2.2 μm). It combines the light from four Unit Telescopes (UTs) or Auxiliary Telescopes (ATs), measuring the interferograms from six baselines simultaneously. The instrument has three main components: the IR wavefront sensors; the beam-combiner instrument; and the laser metrology system.
The GRAVITY IR wavefront sensors will be mounted in the Coudé rooms of the UTs and will command the existing Multiple Application Curvature Adaptive Optics (MACAO) deformable mirrors. The system can work on either of the two beams (on-axis or off-axis) behind the PRIMA star separators. Any additional tip/tilt from the beam relay down to the VLTI laboratory will be corrected by a dedicated laser-guiding system. Low frequency drifts of the field and pupil will
be corrected by GRAVITY’s internal acquisition and guiding camera. The interplay of these systems will guarantee an unperturbed and seeing-corrected beam at the entrance of the beam-combiner instrument in the VLTI laboratory. The interferometric instrument will work on the 2” (for UTs) or 4” (for ATs) VLTI field of view. Both the reference star and the science object have to lie within this field of view. The light of the two objects from the four telescopes is coupled into optical fibres for modal filtering, to compensate for the differential delay and to adjust the polarisation. The fibres feed two integrated optics beam combiners and the coherently combined light is dispersed in two spectrometers. A low resolution spectrometer provides internal phase- and group-delay tracking on the reference star, and thus enables long exposure times on the science target. Three spectral resolutions with up to R~4000 are implemented in the science spectrometer, and a Wollaston prism provides basic polarimetry.

Do I understand this?

hey Moll. Hubble got that pic of Neptunes vortex! Hubble just found a ‘dark vortex’ on Neptune

Postpocelipse said:

hey Moll. Hubble got that pic of Neptunes vortex! Hubble just found a ‘dark vortex’ on Neptune

Shouldn’t the net global drag between a gas giant’s atmosphere and that of a compound surface require that a ratio of the atmosphere must travel at a relative velocity to the surface, making these vortexes inevitable and permanent?

Postpocelipse said:

Postpocelipse said:

hey Moll. Hubble got that pic of Neptunes vortex! Hubble just found a ‘dark vortex’ on Neptune

Shouldn’t the net global drag between a gas giant’s atmosphere and that of a compound surface require that a ratio of the atmosphere must travel at a relative velocity to the surface, making these vortexes inevitable and permanent?

I think that might even provide a basis for how solar flares erupt.

Postpocelipse said:

Postpocelipse said:

Postpocelipse said:

hey Moll. Hubble got that pic of Neptunes vortex! Hubble just found a ‘dark vortex’ on Neptune

Shouldn’t the net global drag between a gas giant’s atmosphere and that of a compound surface require that a ratio of the atmosphere must travel at a relative velocity to the surface, making these vortexes inevitable and permanent?

I think that might even provide a basis for how solar flares erupt.

Provided the heliosphere is factored as the stratospheric extent of a solar atmosphere, I think.

Postpocelipse said:

hey Moll. Hubble got that pic of Neptunes vortex! “Hubble just found a ‘dark vortex’ on Neptune.

Shouldn’t the net global drag between a gas giant’s atmosphere and that of a compound surface require that a ratio of the atmosphere must travel at a relative velocity to the surface, making these vortexes inevitable and permanent?

I think that might even provide a basis for how solar flares erupt.

Nice picture!

Gas giants like Neptune don’t have a well-defined surface, compound or otherwise. Instead, there is a slow transition from gaseous upper layers into supercritical lower layers. At the pressures in the lower layers the boundary between gas and liquid disappears and instead the fluid just slowly gets more dense and slowly less compressible.

There ought to be energy loss due to fluid viscosity, meaning that the vortices ought to dissipate. The rate of dissipation ought to be much slower than that of an Earthly hurricane because the energy loss on Earth due to the drag of the gas on the water/ground surface below on Earth is absent on Neptune.

But even on Neptune (and the Sun) there needs to be an energy source driving these vortices. For the Sun the energy source is obvious, for Neptune it isn’t. I don’t know if anyone has yet solved the problem of where Neptune’s energy comes from.

> ie. they’re not observing the black hole itself, only the star in orbit around it. Fingers crossed that they can also see the black hole.

I think I’m wrong there. They are trying to see both the black hole and the adjacent star. They are using a guide star nearby to correct for atmospheric turbulence in a patch 0.5 arcseconds across (which is small by anyone’s definition) that includes the black hole. It hadn’t occurred to me before that correcting for atmospheric turbulence on a high resolution interferometer must be an order of magnitude more difficult than correcting for atmospheric turbulence on a standard astronomical photograph.