Search results for: job geheniau

Using an RTL-SDR to Measure the Basis for the Dark Matter Hypothesis

From calculations depending on the distribution of visible star mass in our galaxy, a certain galactic rotational velocity vs distance from center curve is expected. However, when scientists actually measure the galactic rotation, another curve is found - a curve which should result in the galaxy flying apart. This mismatch in expected vs measured data has given rise to the theory of "dark matter". The theory essentially states that in order to get the measured curve, the galaxy must have more mass, and that this mass must come from non-luminous matter scattered amongst the galaxy which is difficult or impossible to observe.

In the past we have posted about Job Geheniau's radio astronomy projects a few times on this blog. So far he has used an RTL-SDR and radio telescope dish to generate a full radio image of the galaxy at the Hydrogen Line frequency of 1.42 GHz. This project worked by pointing the telescope at one section of the galaxy, measuring the total Hydrogen line power with the RTL-SDR over a number of minutes, then moving the telescope to the next section.

Job's Radio Telescope + Laptop and RTL-SDR Setup

Using the same hardware and techniques to observe the Hydrogen Line frequency, he was now able to measure the rotational curve of our galaxy. When the telescope points to different arms of the galaxy, the Hydrogen line measurement will be doppler shifted differently. The measured doppler shift can be used to figure out the rotational velocity of that particular arm of the galaxy. By measuring the rotational velocity from the center of the galaxy to the outer edges, a curve is created. Job's measured curve matches that seen by professional radio astronomers, confirming the mismatch in expected vs measured data.

Job's document explaining his setup and measurement procedure can be found here (pdf file).

Job's Measured vs Expected Curve

If you'd like to get started with Hydrogen line radio astronomy with an RTL-SDR, we have a tutorial over here.

Imaging the Milky Way in Neutral Hydrogen with an RTL-SDR Part 2

Last month we shared information about Job Geheniau's success with using an RTL-SDR dongle to image our galaxy in neutral Hydrogen. Our galaxy is full of neutral Hydrogen, and lots of neutral Hydrogen together results in a detectable radio peak at 1.42 GHz. This peak is called the Hydrogen line. By scanning the galaxy at the Hydrogen line frequency with a 1.5 meter dish on a motorized mount, an RTL-SDR, and a few filters and LNAs, Job is able to create a radio image of our galaxy.

In Job's previous attempt he created an image by pointing the dish antenna at 168 predefined grids calculated to cover the Milky Way, resulting in 168 points of exposure data. In his latest work Job has created an even higher resolution image by taking 903 points of exposure data. Each exposure took 150s and the total 903 exposures took 8 nights to record. Once all data was collected he uses the same process as before, which is to input all the Hydrogen line data into a standard 2D excel sheet, then use conditional formatting to create a heatmap which reveals the image. He then applies a blur and stretches the image into the Mollweide Cartographic which can represent the entire Universe in one image.

Job has shared with us his PDF where he documented his process and shares his images (note 16 MB PDF file). We also share his full resolution images below, just click to open. We think that these images are quite amazing and an excellent achievement for a backyard radio astronomer.

If you're interested in Hydrogen line radio astronomy we have a tutorial that will help you observe the Hydrogen line peak on a budget. The tutorial could be improved upon by motorizing the dish, allowing you to create images like the ones above. You might also be interested in a similar project by Marcus Leech who took 5 months of hydrogen line observations with an RTL-SDR in order to create an even higher resolution image.

Imaging the Milky Way in Neutral Hydrogen with an RTL-SDR

Over on Facebook Job Geheniau has recently been sharing how he's taken an image of our galaxy (the Milky Way) with a radio telescope consisting of a 1.5 meter dish, RTL-SDR and a few filters and LNAs. In the past we've posted several times about others observing the Hydrogen line with an RTL-SDR, and we have a tutorial here showing how to observe it on a budget.

In this case, Job went a step further than just a single measurement. He used a used a motorized dish and RTL-SDR to scan the entire Milky Way over one month, resulting in a full radio image of the galaxy. As his posts and pdf document are on Facebook and not visible to those without Facebook accounts, we asked for permission to reproduce some of them here for all to see. We have also mirrored his PDF file here, which contains more information about his radio telescope, results and setup.

To make a very long story short. After a month of angel patience (and that says something to me) I managed to take a 'picture' of our entire galaxy (galaxy) in neutral hydrogen! I attach some pictures. If you are more interested, please come after this and PDF with explanation. It was a hell of a job I can tell you. But here's the ' picture s' of the house (230 million light years wide) in which we live and in which we all have a big mouth......

Hydrogen Line Image of the Milky Way produced by Job Geheniau
Hydrogen Line Image of the Milky Way produced by Job Geheniau

For the Scientists among us... a beautiful plot of the Milky Way Graphically explained in neutral hydrogen....... In short, summarized... if you look up on a beautiful summer evening you will see a beautiful galaxy, this is graphically the same but then on a different frequency than the eye can perceive. own dates of course.....

A composite of Hydrogen Line readings at different points of the Milky Way
A composite of Hydrogen Line readings at different points of the Milky Way produced by Job Geheniau
An image of the Galactic Plane (longitude 20 to 240 steps of 5 degrees and latitude 0)
An image of the Galactic Plane (longitude 20 to 240 steps of 5 degrees and latitude 0)

His setup consists of a 1.5m dish, extended to 1.9m with some mesh. A 1420 MHz tuned feed, Mini Circuits ZX6-P33ULN LNA, Bandpass Filter, NooElec SAWBird LNA, Bias-T, RTL-SDR V3, PST Rotator Dish Software, VIRGO software, SDR#, Cartes due Ciel sky chart and a home made netfilter.

He uses a modified version of the VIRGO software to read sky coordinates from a text file, and this points the telescope at each predefined coordinate. He then uses VIRGO to record data for 180 seconds before moving on to the next coordinate. The data is then plotted in Excel, and the highest peak is taken at each coordinate and put back into an 8x21 matrix in excel. Conditional formatting is then used to generate a color gradient resulting in a rough map. Then a Gaussian blur is applied, and it is projected over the Galaxy, resulting in the images above.

Job Geheniau's Radio Telescope Setup
Job Geheniau's Radio Telescope Setup

In the past we've seen a very similar project performed by Marcus Leech from ccera.ca. However, his measurements use 5 months of observations resulting in much higher resolution data.

The Hydrogen Line is an observable increase in RF power at 1420.4058 MHz created by Hydrogen atoms. It is most easily detected by pointing a directional antenna towards the Milky Way as there are many more hydrogen atoms in our own galaxy. This effect can be used to measure the shape and other properties of our own galaxy.