4 ms·

I'm a scientist on the team who did this (I actually helped put this picture together), so I can try to answer questions...

by xioxox 6y ago

someguydave 6y ago
Has the eROSITA mission discovered any previously unknown black holes?
- xioxox 6y ago
  Lots! It has discovered about a million X-ray sources, about twice as many as previously known about. Most of these sources will be active galactic nuclei (supermassive black holes that are accreting material) in distant galaxies. There's still lots of work to do in characterising these objects though and understanding the population.
SiempreViernes 6y ago
The Fermi bubbles are super-prominent, is eROSITA the first x-ray telescope sensitive to detect them?
- xioxox 6y ago
  Some of the structure can be seen in the old ROSAT maps from the 90s: http://www.xray.mpe.mpg.de/rosat/survey/sxrb/12/ass.html http://www.xray.mpe.mpg.de/rosat/survey/sxrb/12/ass.html Recently XMM looked at the centre of the galaxy, finding chimney-like structures which may link to the bubbles. This is on a much smaller region, however: http://www.esa.int/Science_Exploration/Space_Science/Giant_chimneys_vent_X-rays_from_Milky_Way_s_core http://www.esa.int/Science_Exploration/Space_Science/Giant_c... Nothing since ROSAT has had the ability to map large areas like eROSITA/SRG. ABRIXAS was supposed to be the successor to ROSAT, but it failed shortly after launch.
SiempreViernes 6y ago
And what is the angular resolution of the real thing?
- xioxox 6y ago
  The half energy width (angle over which half the energy is deposited) is around 16 arcsec on the axis of the telescopes (3600 arcsec=1 deg). Due to the Wolter geometry, it gets worse as you go off-axis. In the survey sources scan over the field of view. The average survey performance is around 28 arcsec.
spodek 6y ago
I helped build and calibrate XMM, earning my PhD https://www.researchgate.net/publication/252418991_The_X-ray_observational_satellite_XMM_its_spectrometer_and_observations_of_supernova_remnants https://www.researchgate.net/publication/252418991_The_X-ray... in the 90s, before leaving academia to start my first company. I haven't kept track of the field. Has eROSITA reproduced most of XMM's data? I expect XMM will keep collecting data, but how useful/obsolete has it become?
- xioxox 6y ago
  XMM is still extremely useful. There was a recent report that using clever techniques ESA are going to keep it going for another 10 years: https://www.esa.int/Enabling_Support/Operations/Teaching_an_old_satellite_new_tricks https://www.esa.int/Enabling_Support/Operations/Teaching_an_... XMM has a smaller field of view than eROSITA, but more light gathering capability (effective area), particularly at higher energies. It also has different types of instruments, such as the X-ray gratings. eROSITA is really designed for doing surveys with its wide unobstructed field of view, and it will be doing just that for the next 3.5 yrs. We really need XMM to follow up in detail the most interesting sources we discover during the survey.
xioxox 6y ago
Here's a nice video showing how SRG/eROSITA scans the sky: https://www.youtube.com/watch?v=z8M-80aMDO0 https://www.youtube.com/watch?v=z8M-80aMDO0
staycoolboy 6y ago
How does this align with expectations, meaning more or fewer X-ray sources? What's the biggest "Holy -----!" moment after viewing the results? (Other than the fact that after 182 days of data collection you produced this astonishing map!) I'm interpreting this as a picture of all massive X-ray sources in the visible universe. And I'm kinda ... sad? that it looks so empty....? But at the same time I'm also thrilled by each and every point.
- xioxox 6y ago
  I believe it's detecting more sources than expected. This can be to do with how efficient observations are (very good so far), how low the background is (higher than expected, but stable), the performance of the telescope in space, and how good the simulations of the data are (we're still working on them!). I was very impressed with the picture of the Shapley supercluster (see article), which is very overdense part of the local universe, containing dozens of clusters of galaxies, each of those with 100s to 1000s of galaxies. In addition, we took some performance verification observations at the start, and these were really nice: http://www.mpe.mpg.de/7362095/news20191022 http://www.mpe.mpg.de/7362095/news20191022 The picture is a bit misleading about the number of sources. It's really dominated by our galaxy, as most sources are point-like. You cannot really see the majority of them individually in the full-sky map given its spatial resolution, particularly as we applied some smoothing to the data to help emphasise the galactic structure. We're also going to get another 3.5 years more data in the survey, which is going to find a lot more sources.

I'm a scientist on the team who did this (I actually helped put this picture together), so I can try to answer questions...

by xioxox 6y ago

I'm a scientist on the team who did this (I actually helped put this picture together), so I can try to answer questions...

someguydave 6y ago

Has the eROSITA mission discovered any previously unknown black holes?

xioxox 6y ago
Lots! It has discovered about a million X-ray sources, about twice as many as previously known about. Most of these sources will be active galactic nuclei (supermassive black holes that are accreting material) in distant galaxies. There's still lots of work to do in characterising these objects though and understanding the population.

SiempreViernes 6y ago

The Fermi bubbles are super-prominent, is eROSITA the first x-ray telescope sensitive to detect them?

xioxox 6y ago
Some of the structure can be seen in the old ROSAT maps from the 90s: http://www.xray.mpe.mpg.de/rosat/survey/sxrb/12/ass.html http://www.xray.mpe.mpg.de/rosat/survey/sxrb/12/ass.html Recently XMM looked at the centre of the galaxy, finding chimney-like structures which may link to the bubbles. This is on a much smaller region, however: http://www.esa.int/Science_Exploration/Space_Science/Giant_chimneys_vent_X-rays_from_Milky_Way_s_core http://www.esa.int/Science_Exploration/Space_Science/Giant_c... Nothing since ROSAT has had the ability to map large areas like eROSITA/SRG. ABRIXAS was supposed to be the successor to ROSAT, but it failed shortly after launch.

SiempreViernes 6y ago

And what is the angular resolution of the real thing?

xioxox 6y ago
The half energy width (angle over which half the energy is deposited) is around 16 arcsec on the axis of the telescopes (3600 arcsec=1 deg). Due to the Wolter geometry, it gets worse as you go off-axis. In the survey sources scan over the field of view. The average survey performance is around 28 arcsec.

spodek 6y ago

I helped build and calibrate XMM, earning my PhD https://www.researchgate.net/publication/252418991_The_X-ray_observational_satellite_XMM_its_spectrometer_and_observations_of_supernova_remnants https://www.researchgate.net/publication/252418991_The_X-ray... in the 90s, before leaving academia to start my first company. I haven't kept track of the field. Has eROSITA reproduced most of XMM's data? I expect XMM will keep collecting data, but how useful/obsolete has it become?

xioxox 6y ago
XMM is still extremely useful. There was a recent report that using clever techniques ESA are going to keep it going for another 10 years: https://www.esa.int/Enabling_Support/Operations/Teaching_an_old_satellite_new_tricks https://www.esa.int/Enabling_Support/Operations/Teaching_an_... XMM has a smaller field of view than eROSITA, but more light gathering capability (effective area), particularly at higher energies. It also has different types of instruments, such as the X-ray gratings. eROSITA is really designed for doing surveys with its wide unobstructed field of view, and it will be doing just that for the next 3.5 yrs. We really need XMM to follow up in detail the most interesting sources we discover during the survey.

xioxox 6y ago

Here's a nice video showing how SRG/eROSITA scans the sky: https://www.youtube.com/watch?v=z8M-80aMDO0 https://www.youtube.com/watch?v=z8M-80aMDO0

staycoolboy 6y ago

How does this align with expectations, meaning more or fewer X-ray sources? What's the biggest "Holy -----!" moment after viewing the results? (Other than the fact that after 182 days of data collection you produced this astonishing map!) I'm interpreting this as a picture of all massive X-ray sources in the visible universe. And I'm kinda ... sad? that it looks so empty....? But at the same time I'm also thrilled by each and every point.

xioxox 6y ago
I believe it's detecting more sources than expected. This can be to do with how efficient observations are (very good so far), how low the background is (higher than expected, but stable), the performance of the telescope in space, and how good the simulations of the data are (we're still working on them!). I was very impressed with the picture of the Shapley supercluster (see article), which is very overdense part of the local universe, containing dozens of clusters of galaxies, each of those with 100s to 1000s of galaxies. In addition, we took some performance verification observations at the start, and these were really nice: http://www.mpe.mpg.de/7362095/news20191022 http://www.mpe.mpg.de/7362095/news20191022 The picture is a bit misleading about the number of sources. It's really dominated by our galaxy, as most sources are point-like. You cannot really see the majority of them individually in the full-sky map given its spatial resolution, particularly as we applied some smoothing to the data to help emphasise the galactic structure. We're also going to get another 3.5 years more data in the survey, which is going to find a lot more sources.