Hubble vs Webb

Hubble composite SMACS 0723
Webb composite SMACS 0723

The above images of galaxy cluster SMACS 0723 (located 4.6 billion light years away) highlights the huge resolution jump from Hubble to Webb.

Webb’s first full colour image took just 12.5 hours of integration time to capture and already reveals detail surpassing Hubble’s deepest field images, some of which took weeks of accumulated processing time.

The area of space imaged in this composite is equivalent to holding a grain of sand to the night sky at arms length. Almost all the individual points of light here are separate and independent galaxies, each containing 100s of billions of stars, and captured in various stages of historical morphology going back as far as 13 billion years (due to the help of gravitational lensing).

While greater mirror diameter and enhanced sensor resolution accounts for much of the extra clarity Webb has over Hubble, it should be remembered that James Webb is an Infrared telescope, so less detail in its deep field images gets obscured by opaque interstellar dust, which can block some of the visible wavelengths of light Hubble sees. Also, visible light that has experienced extreme red shifts (due to the expansion of the universe) can end up stretched into the Infrared, so Webb can look much further back in time than Hubble, revealing some of the oldest first generation galaxies yet seen.

Belladrum 2022 Night Sky Show

I’m delighted to be hosting my Night Sky Show at the 2022 Belladrum Festival again from 28th – 30th July at 11pm. Learn about galaxies, stars, planets, meteors, satellites and the astonishing history and enormity of our Cosmos.

There’s no Boffinarium this year so my presentation will be located outdoors with laser pointer under twilight skies, with backup projector and screen. Stay tuned for times and festival location.

Our Supermassive Black Hole – Sagittarius A

Sagittarius A – as imaged by the team at the Event Horizon Telescope.

Imagine taking over 4 million copies of our Sun and cramming the combined mass into a region of space no bigger than the orbit of Mercury.

That’s Sagittarius A, the supermassive black hole at the centre of our own Milky Way galaxy. Evidence for Sagittarius A has been growing since the 1970s but now in 2022 the team at the Event Horizon Telescope have actually imaged it.

The term ‘supermassive’ when attributed to black holes is very misleading as black holes are incredibly low volume but dense regions of space. To give you a feel for this, if you took our Moon and somehow compressed it into a black hole, the resulting anomaly would have a diameter of 0.2 millimetres! That’s probably less than the size of a single pixel on the screen you’re reading this article on.

As black holes grow they can devour more mass and will slowly get bigger with the event horizon radius r defined by the famous Schwarzschild equation:

r = 2GM/c^2

In this equation G is the universal gravitational constant, c is the speed of light and M is the mass of the black hole. This is a simple linear relationship, so for example doubling the mass of a black hole will double its radius.

The bright central region of our Milky Way galaxy where Sagittarius A is located. Telescopes of the Atacama Large Millimeter/submillimeter Array in the foreground. Credit: EHT Collaboration

Given the relatively small volumes and areas of space involved, detecting even the most massive black holes in challenging to say the least. Sagittarius A, despite containing millions of solar masses, occupies a volume smaller than a single star in its giant phase of evolution. This gets compounded by the incredible distances involved. The centre of our Milky Way where Sagittarius A is located is a staggering 26,000 light years away. How then did the team capture the image?

The key was using multiple detectors spread across the planet, effectively constructing an Earth sized telescope. The data collected from these widely spaced arrays was then gathered together, producing many terabytes of data, and processed by banks of supercomputers called ‘correlators’. The final image was constructed using advanced algorithmic and statistical imaging techniques.

EVT’s detectors are spread around the planet effectively creating an Earth sized detection aperture.

Clearly by their nature black holes do not allow any light to escape so what we see in the final image is the infrared signature of super-heated gas rotating close to the black hole.  Black holes therefore reveal themselves by their indirect influence on nearby objects rather than direct observation.

Indeed, Sagittarius A’s existence was originally inferred by its influence on nearby stars, which are being thrown about at fantastically high speeds due to its intense gravitational influence. Fast enough for us to produce time lapse images over several years (see animation below).

Time-lapse from the ESO’s Very Large Telescope in Chile shows stars orbiting close to Sagittarius A over a 20 year detection period. 

Donated 200mm Telescope for Abriachan

Fully restored Sky-Watcher 200mm telescope for Abriachan Forest

I recently restored a lovely 200mm reflector, kindly donated to our astronomy programme at Abriachan Forest. This one came from @BigSkyLodges over in the Black Isle. Many thanks to Martin Hind for the heads up.

Just needed a clean and some TLC and now back in good working order. This adds to our 150mm reflector and will compliment our binocular stargazing events when we kick off next season.  

A 200mm like this is ideal for observing fainter deep sky objects like galaxies, planetary nebulae and globular clusters. 

Stargazing at the End of Night

Sunset over Glen Docherty

This was me on the road and heading into the western Highlands last Saturday for my final stargazing gig of the season with the Woodland Trust.  

Skies this far north will shortly be too bright to stargaze with only Astronomical Twilight levels of darkness left near midnight and no official ‘night’ again until mid to late August. So do get out while you still can.  Of course the further south you are the less impacted you will be by this ‘near’ midnight Sun.

I had an eventful stargazing session with the Woodland Trust who were based at the Torridon for several nights. We first headed outside at about 10.30pm to view the crescent Moon with binoculars during early twilight skies – still too bright to see many stars apart from brilliant Arcturus.

The spring star Arcturus ‘Bear Watcher’ was bright enough to see in early twilight during our Moon gazing session.

After heading back inside for more projector based astronomy we ventured outside once more after 11pm and were fortunate to see a decent collection of bright stars and constellations despite some hazy cloud overhead.

Vega, Capella, Arcturus and Spica were all visible, in addition to the main stars in the Plough. I’d like to thank the Woodland Trust for inviting me and wish them well in their rewilding endeavours across the Highlands.