This month I'm making time to learn new skills. Continuing with my interest in machine learning and data science has to be somewhat extracurricular, because my current research project doesn’t really call for it. Well, I’m doing “regression analysis” by fitting models to data, but I’m not really practicing any of the ML techniques that I learned about last August at the data science summer school I attended, e.g., classification (incidentally, S2DS is currently accepting applications for this year’s class).
To learn some new skills, I’ve been spending 1 hour per day with the book Statistics, Data Mining, and Machine Learning in Astronomy by Z. Ivezic, A. Connolly, J. VanderPlas, and A. Gray (note they use the Oxford comma - let that be a lesson to you). This book is also known as AstroML.
The book is divided into two parts, and I’ve decided to work through it by bouncing between them. I’m not sure it is the most efficient way to work through it, but I think it will keep my interest longer. I’ve worked through Chapters 1 & 2, and now I’m working through Chapter 6. After that, I'll got back to Chapter 3, and so on. A research partner of mine and I have some ideas that we want to use ML techniques for. Hopefully this book will teach us how to do that.
There is a website that accompanies the book, astroml.org, and it contains the code for the figures found within. We are working through those, trying to understand as best we can, so we can implement similar techniques in our research.
This project has two main goals for me. The first, as stated above, is that it is interesting and will lead to some interesting research. The second is that it will really help develop my professional skills. I’m still waiting to hear back from a couple positions that I applied to, but I’m also starting to diversify my applications. In February, I’ve applied to 11 positions in industry so far - that’s in addition to the 20+ academic positions that I applied to during the Nov-Jan period. The academic application period is slowing down now, so if I really want to come back to the U.S. anytime soon, I’ll need to diversify.
That’s what’s new with me,
Kyle
Friday, February 20, 2015
Sunday, January 25, 2015
A Collaborative Visit
I’ve just returned from a visit to Middlebury College in Vermont, where I gave a talk and visited with a collaborator.
During my graduate work, I ended up with some extra data. I had applied for observations of a sample of red quasars several years in a row and was denied time. On the third time, I/we were granted time to observe these objects with NASA’s Infrared Telescope Facility on Mauna Kea in Hawaii. This was really great, but by that time I was ready to graduate. I went observing and took the data, but they did not make it into my Ph.D. thesis. Instead, my advisor and I decided to give the data to someone who is an expert in red quasars, and she was glad to have the data.
Since then the data have been reduced and our collaborator let a student work on some of the analysis. The student calculated black hole masses from the spectra that I observed, plus a series of other spectra that were not mine in origin. And since I am currently visiting Yale University in New Haven, CT, I thought it would be easy to drive up to Middlebury, VT for a visit and status update on the infrared spectra. It turns out the student did a lot of great work, and we are looking forward to turning her work into a publication.
While at Middlebury College I was asked to give a talk. Academic astronomy talks are usually somewhere between 30 min and 1 hour, depending on the level of formality. The one exception is that at the American Astronomical Society meetings, you only get 5 minutes to present your current research. Those meetings are just so big that there is no way to give people more time. Anyway, I put together my slides during the couple days before actually going to Middlebury. I was a bit hesitant at first, because I haven’t given a presentation recently and I felt out of practice. But, that also was a strong motivator.
It turned out really well. I got a lot of positive feedback from several people in the audience, and I got a lot of questions after the talk. I was very happy to receive the feedback, because I was a little nervous going into the presentation.
After the talk, we had a little group meeting between the collaborators on the red quasar project. It went really well, and I was impressed by the amount of work that the student had done, who is an undergraduate. And those discussions naturally led into discussions about a future project. I will write a proposal to observe these objects with a facility in Chile, which I think will be really useful to learn about the physics that is going on in this sample and will tell us about black hole - galaxy evolution.
So that’s my update for the week. It was a good week.
Oh yeah - Airbnb and poutine are really good - although, not necessarily related.
During my graduate work, I ended up with some extra data. I had applied for observations of a sample of red quasars several years in a row and was denied time. On the third time, I/we were granted time to observe these objects with NASA’s Infrared Telescope Facility on Mauna Kea in Hawaii. This was really great, but by that time I was ready to graduate. I went observing and took the data, but they did not make it into my Ph.D. thesis. Instead, my advisor and I decided to give the data to someone who is an expert in red quasars, and she was glad to have the data.
Since then the data have been reduced and our collaborator let a student work on some of the analysis. The student calculated black hole masses from the spectra that I observed, plus a series of other spectra that were not mine in origin. And since I am currently visiting Yale University in New Haven, CT, I thought it would be easy to drive up to Middlebury, VT for a visit and status update on the infrared spectra. It turns out the student did a lot of great work, and we are looking forward to turning her work into a publication.
While at Middlebury College I was asked to give a talk. Academic astronomy talks are usually somewhere between 30 min and 1 hour, depending on the level of formality. The one exception is that at the American Astronomical Society meetings, you only get 5 minutes to present your current research. Those meetings are just so big that there is no way to give people more time. Anyway, I put together my slides during the couple days before actually going to Middlebury. I was a bit hesitant at first, because I haven’t given a presentation recently and I felt out of practice. But, that also was a strong motivator.
It turned out really well. I got a lot of positive feedback from several people in the audience, and I got a lot of questions after the talk. I was very happy to receive the feedback, because I was a little nervous going into the presentation.
After the talk, we had a little group meeting between the collaborators on the red quasar project. It went really well, and I was impressed by the amount of work that the student had done, who is an undergraduate. And those discussions naturally led into discussions about a future project. I will write a proposal to observe these objects with a facility in Chile, which I think will be really useful to learn about the physics that is going on in this sample and will tell us about black hole - galaxy evolution.
So that’s my update for the week. It was a good week.
Oh yeah - Airbnb and poutine are really good - although, not necessarily related.
Monday, January 19, 2015
A Quick Update
Recently I attended the American Astronomical Society’s 225th conference in Seattle, WA. Even though the conference is a week long, I was only in attendance for one day.
I had a great time on my one day in Seattle; it was very full, and several people stopped by to see my poster. I also had meetings with other astronomers from around the country.
One encounter stuck out while speaking with someone at my poster. Even though he and I had an interest in the same science, he had never heard of me, nor seen my work. I actually expect this when I encounter people. I am under no illusion that my papers stand out from the dozens that get posted on astro-ph every day. Furthermore, I only have a small few papers. So, I was not surprised when he did not know me. By chance, I recalled his name from having read his paper, so in that way it was a little lopsided.
In any case, my point is that he would never have seen my work if I had not met him at the conference. We had a good conversation, and because he seemed genuinely interested, I followed up with him by sending an email the week after the conference.
The week after the conference I was laid out with a cold. This was very frustrating for me, because I couldn’t focus on anything to get work done. I did manage to bring my wits about me enough to apply for a couple jobs, so that was productive.
Speaking of . . . I’m really hoping to get a good job offer this year, because I’m trying to solve a two-body problem. Even though the nature of post-doc-hood and academia isn’t particularly partner friendly, I have to say that the people I have met within astronomy have all been understanding of the issue and have tried to be flexible to accommodate my situation.
This week I plan to go visit a colleague at another university. I am hoping to brainstorm a good ALMA proposal to take advantage of my Chilean observer status. While I am there I will give a talk to a general science audience. I like these kinds of talks, because they tend to be concept-oriented. I am looking forward to the week, but putting together the talk will take a bit of time. Next week I will have to get back to my narrow-line seyfert 1 data, so I can have some good results for the upcoming conference in March!
Phew, catch ya later
I had a great time on my one day in Seattle; it was very full, and several people stopped by to see my poster. I also had meetings with other astronomers from around the country.
One encounter stuck out while speaking with someone at my poster. Even though he and I had an interest in the same science, he had never heard of me, nor seen my work. I actually expect this when I encounter people. I am under no illusion that my papers stand out from the dozens that get posted on astro-ph every day. Furthermore, I only have a small few papers. So, I was not surprised when he did not know me. By chance, I recalled his name from having read his paper, so in that way it was a little lopsided.
In any case, my point is that he would never have seen my work if I had not met him at the conference. We had a good conversation, and because he seemed genuinely interested, I followed up with him by sending an email the week after the conference.
The week after the conference I was laid out with a cold. This was very frustrating for me, because I couldn’t focus on anything to get work done. I did manage to bring my wits about me enough to apply for a couple jobs, so that was productive.
Speaking of . . . I’m really hoping to get a good job offer this year, because I’m trying to solve a two-body problem. Even though the nature of post-doc-hood and academia isn’t particularly partner friendly, I have to say that the people I have met within astronomy have all been understanding of the issue and have tried to be flexible to accommodate my situation.
This week I plan to go visit a colleague at another university. I am hoping to brainstorm a good ALMA proposal to take advantage of my Chilean observer status. While I am there I will give a talk to a general science audience. I like these kinds of talks, because they tend to be concept-oriented. I am looking forward to the week, but putting together the talk will take a bit of time. Next week I will have to get back to my narrow-line seyfert 1 data, so I can have some good results for the upcoming conference in March!
Phew, catch ya later
Tuesday, December 23, 2014
Astronomers - Where are we going and who will we be when we get there?
Let’s talk about the US Bureau of Labor Statistics report on Physicists and Astronomers.
Here’s the link:
http://www.bls.gov/ooh/life-physical-and-social-science/physicists-and-astronomers.htm
First note the median pay of a physicist or astronomer: $106,360 per year. Honestly I find this number laughably large. You can scroll down and find that the breakdown is actually physicists’ median = $106,840, while astronomers’ median = $96,460, which is still large, in my opinion. Let’s just focus on astronomers here. I think it is a bit misleading to lump physicists and astronomers together; I haven’t heard of many people switching between these two research fields — not without a great deal of effort.
The “median”, by the way, is a kind of average of a set of numbers. It is defined as the number in the middle when you list the set in increasing order. You may be more familiar with the mean average (sum of the set divided by the number of items within the set). The median is less susceptible to being dragged up or down by large outliers in the group. For example, the median of 1, 5, and 10 is 5. If the set were 1, 5, and 10000, the median would still be 5, because it is the middle number. Whereas, the mean average would change a lot.
So I wonder - what is going on here? Surely they are not counting post-docs among this group of astronomers.
Let’s go to the “Work Environment” tab. Here we find that in 2012 the number of astronomers was 2,700 jobs (and physicists was 20,600). This immediately explains why the overall median salary is biased toward a higher number - the physicists make more money and there are more of them than astronomers. But still - 2,700 is a low number of jobs. I suspect that they are only counting faculty, let’s check the breakdown:
54% of astronomers work in colleges, universities, and professional schools.
21% work in research and development in the physical, engineering, or life sciences.
19% are employed by the federal government.
This leaves about 6% unaccounted for. So, a little more than half of astronomers are actually faculty members. If that’s surprising at all, it’s because it seems low to me (excluding post-docs and grad students). About 1/5 of astronomers are employed in research and development. Presumably this is outside of colleges and universities, and outside government entities. I suppose this could include observatory staff astronomers, but my perception is that they make up more like 10% rather than 20% of the community. Is it possible that the post-docs are included in the 21% category? Post-docs are mentioned in the “How to Become One” tab:
“Many physics and astronomy Ph.D. holders who seek employment as full-time researchers begin their careers in a temporary postdoctoral research position, which typically lasts 2 to 3 years. During their postdoctoral appointment, they work with experienced scientists as they continue to learn about their specialties or develop a broader understanding of related areas of research. Their initial work may be carefully supervised by senior scientists, but as they gain experience, they usually do more complex tasks and have greater independence in their work.”
All true, but let’s not keep post-docs down. In my opinion, a Ph.D. graduate is fully qualified to become a faculty member straight away. That’s not true for everyone, but for many I think it is. The fact that post-doc positions are common now is due to there not being enough permanent faculty spots to go around. There’s an oversupply of qualified people, and an under-supply of positions.
As an aside there is probably demand for a whole new set of faculty; there are plenty of undergraduate students who want to learn physics and astronomy. There just isn’t enough funding to support those faculty. And everyone loses a little bit. Write your senators, folks.
“Pay” tab.
“The median annual wage for astronomers was $96,460 in May 2012. The lowest 10 percent earned less than $51,270, and the top 10 percent earned more than $165,300.”
If you are lucky enough to get a job offer in astronomy, use this information to negotiate your salary. Be a little careful when quoting these numbers, though, because the breakdown shows a stark contrast between university employees and federal employees.
Federal employees are the highest paid with a median of $139,000 per year, but only make up 19% of astronomers. University and college faculty, while making up the majority of astronomers, are only making a median of ~$78,000 per year. Still useful info for that initial salary negotiation.
So realistically if you get to be a tenured faculty member, you still aren’t going to make the overall median salary, because the median is being brought up by the federal employees — despite the median being robust against outliers (~20% is not an outlier).
Let’s take a look at the “Job Outlook” tab, and here’s the kicker. During the 10-year period from 2012-2022, the federal government expects the growth rate for astronomers to be 10%. With a population of 2,700, that means we can expect 270 new jobs in 10 years. That’s probably not counting the replacement of people who retire, so let’s be generous and throw those in there too. Call it 350 jobs over 10 years. That’s really generous, because the number that is actually projected on the website is 300 jobs. Also note that the projected employment in 2022 is 2,900, which is 200 greater than 2,700, not 300 as is listed in the 'Numeric' column. Hey Bureau of Labor Statistics, 200. / 2700. is 7.4%, not 10% - can we get a little better precision here? Lots of post-docs’ careers depend on this measurement. For being a bureau of statistics, they are remarkably inconsistent.
You know what? There are probably more than 300 post-docs this year looking for permanent jobs. Good luck. You might get hired sometime during the next 10 years.
If you are interested, you might consider browsing some other occupations described by the Bureau of Labor Statistics for comparison. For example, “computer and information research scientists” numbered around 27,000 (ten times that of astronomers) in 2012, and are expected to grow by about 4,000 (15%) between 2012 and 2022. Hey, they also make a median salary of $102,000 per year (~20-30k more than the majority of astronomers). Turns out they have a lot of overlapping skills, too. Just something to think about.
Information and quotes gathered from:
Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, 2014-15 Edition, Computer and Information Research Scientists, on the Internet at http://www.bls.gov/
Here’s the link:
http://www.bls.gov/ooh/life-physical-and-social-science/physicists-and-astronomers.htm
First note the median pay of a physicist or astronomer: $106,360 per year. Honestly I find this number laughably large. You can scroll down and find that the breakdown is actually physicists’ median = $106,840, while astronomers’ median = $96,460, which is still large, in my opinion. Let’s just focus on astronomers here. I think it is a bit misleading to lump physicists and astronomers together; I haven’t heard of many people switching between these two research fields — not without a great deal of effort.
The “median”, by the way, is a kind of average of a set of numbers. It is defined as the number in the middle when you list the set in increasing order. You may be more familiar with the mean average (sum of the set divided by the number of items within the set). The median is less susceptible to being dragged up or down by large outliers in the group. For example, the median of 1, 5, and 10 is 5. If the set were 1, 5, and 10000, the median would still be 5, because it is the middle number. Whereas, the mean average would change a lot.
So I wonder - what is going on here? Surely they are not counting post-docs among this group of astronomers.
Let’s go to the “Work Environment” tab. Here we find that in 2012 the number of astronomers was 2,700 jobs (and physicists was 20,600). This immediately explains why the overall median salary is biased toward a higher number - the physicists make more money and there are more of them than astronomers. But still - 2,700 is a low number of jobs. I suspect that they are only counting faculty, let’s check the breakdown:
54% of astronomers work in colleges, universities, and professional schools.
21% work in research and development in the physical, engineering, or life sciences.
19% are employed by the federal government.
This leaves about 6% unaccounted for. So, a little more than half of astronomers are actually faculty members. If that’s surprising at all, it’s because it seems low to me (excluding post-docs and grad students). About 1/5 of astronomers are employed in research and development. Presumably this is outside of colleges and universities, and outside government entities. I suppose this could include observatory staff astronomers, but my perception is that they make up more like 10% rather than 20% of the community. Is it possible that the post-docs are included in the 21% category? Post-docs are mentioned in the “How to Become One” tab:
“Many physics and astronomy Ph.D. holders who seek employment as full-time researchers begin their careers in a temporary postdoctoral research position, which typically lasts 2 to 3 years. During their postdoctoral appointment, they work with experienced scientists as they continue to learn about their specialties or develop a broader understanding of related areas of research. Their initial work may be carefully supervised by senior scientists, but as they gain experience, they usually do more complex tasks and have greater independence in their work.”
All true, but let’s not keep post-docs down. In my opinion, a Ph.D. graduate is fully qualified to become a faculty member straight away. That’s not true for everyone, but for many I think it is. The fact that post-doc positions are common now is due to there not being enough permanent faculty spots to go around. There’s an oversupply of qualified people, and an under-supply of positions.
As an aside there is probably demand for a whole new set of faculty; there are plenty of undergraduate students who want to learn physics and astronomy. There just isn’t enough funding to support those faculty. And everyone loses a little bit. Write your senators, folks.
“Pay” tab.
“The median annual wage for astronomers was $96,460 in May 2012. The lowest 10 percent earned less than $51,270, and the top 10 percent earned more than $165,300.”
If you are lucky enough to get a job offer in astronomy, use this information to negotiate your salary. Be a little careful when quoting these numbers, though, because the breakdown shows a stark contrast between university employees and federal employees.
Federal employees are the highest paid with a median of $139,000 per year, but only make up 19% of astronomers. University and college faculty, while making up the majority of astronomers, are only making a median of ~$78,000 per year. Still useful info for that initial salary negotiation.
So realistically if you get to be a tenured faculty member, you still aren’t going to make the overall median salary, because the median is being brought up by the federal employees — despite the median being robust against outliers (~20% is not an outlier).
Let’s take a look at the “Job Outlook” tab, and here’s the kicker. During the 10-year period from 2012-2022, the federal government expects the growth rate for astronomers to be 10%. With a population of 2,700, that means we can expect 270 new jobs in 10 years. That’s probably not counting the replacement of people who retire, so let’s be generous and throw those in there too. Call it 350 jobs over 10 years. That’s really generous, because the number that is actually projected on the website is 300 jobs. Also note that the projected employment in 2022 is 2,900, which is 200 greater than 2,700, not 300 as is listed in the 'Numeric' column. Hey Bureau of Labor Statistics, 200. / 2700. is 7.4%, not 10% - can we get a little better precision here? Lots of post-docs’ careers depend on this measurement. For being a bureau of statistics, they are remarkably inconsistent.
You know what? There are probably more than 300 post-docs this year looking for permanent jobs. Good luck. You might get hired sometime during the next 10 years.
If you are interested, you might consider browsing some other occupations described by the Bureau of Labor Statistics for comparison. For example, “computer and information research scientists” numbered around 27,000 (ten times that of astronomers) in 2012, and are expected to grow by about 4,000 (15%) between 2012 and 2022. Hey, they also make a median salary of $102,000 per year (~20-30k more than the majority of astronomers). Turns out they have a lot of overlapping skills, too. Just something to think about.
Information and quotes gathered from:
Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, 2014-15 Edition, Computer and Information Research Scientists, on the Internet at http://www.bls.gov/
Thursday, December 11, 2014
Visiting Yale
My current fellowship is sponsored by the Chilean national government. In particular I hold a FONDECYT Postdoctoral Fellowship. FONDECYT is an acronym for Fondo Nacional de Desarrollo Científico y Tecnológico, which translates to National Fund for Scientific and Technological Development. Naturally, I live and work in Concepción, Chile.
But, thanks to my swank fellowship, I get to be my own boss and decide when and where I go for collaboration. It happens that my current supervisor has close ties to Yale University, and so I’ve extended my network to Yale as well. It also happens that I am part of a two body academic orbit, so coming in close toward Yale is particularly rewarding on a personal level as well as an academic/professional level.
Right now it is early December in New Haven, CT, and I’m in for a nice snowy New England winter; I am staying through the month of February. On my to do list while I am here is to reduce and analyze some spectroscopy of a sample of Narrow-Line Seyfert 1 galaxies. These galaxies host active galactic nuclei (AGN), and are of interest to me because we expect them to have black holes that are smaller than those of other kinds of AGN. We can learn some really neat things about the connections between the AGN and their hosts by studying NLS1s.
I really like the department here. It is big enough that something is going on just about every day. There are lots of scientific talks, or journal clubs, or other social events to attend. I actually have more space here as a visitor, than I do at my home university - I guess being a private institution has benefits. So far I'm enjoying the environment, and I hope to get some good science done while I am here.
I’ll also be traveling to Seattle for the American Astronomical Society meeting in early January. I registered a bit late, and I am only able to present a poster on the last day of the conference, but it is better than nothing. Now I just need to make sure I have those data reduced and ready to show off before then!
In early March I’ll be headed back to Chile, just in time to travel to Puerto Varas for a science meeting. Puerto Varas is a beautiful lake town in the south of Chile, with great views of Volcan Osorno. I’m really looking forward to going back there, and I hope to present some good science results when I am there.
Bye for now!
Tuesday, December 2, 2014
Papers - Proposals to Publishing - Pt 1
I recently published my third first-author paper. It is always a great feeling when a paper gets accepted. As an academic researcher, papers are the primary product of my job. Yes, I have a “real job”. I get paid real money to perform a real service and I output a real product. And yes, this is a point I am defensive about. But to get back on track, this particular paper came out of my graduate work, so it is especially gratifying that it is published.
Publishing a paper is a lot of work. I suppose it is easier for some people or for some disciplines, but I have found it usually to take a significant amount of time and effort. Here is an outline of research from the proposal to the finished paper.
First you have to get an idea for your research project. Then you have to write proposals for either or both funding and data. This process itself can be quite intimidating, but it is often exciting. Writing a proposal is a good time to read papers/research from others and get ideas about what to investigate on your own. I often learn a lot at this stage. After you submit the proposal, it will usually take a few months before the results from the review committee are released. At that point, all you can do is wait - or, more realistically, busy yourself with all the other things you have to do.
Once time/funding/data have been granted you can start your actual research program. Going observing is one of my favorite experiences in astronomy, and maybe I can write up a how-to on observing runs in the future. But let’s say you go observing and collect a bunch of data. Then you get to go home and start analyzing, right? Wrong!
First you have to prepare your data. In astronomy we call this “reducing the raw data”. In other fields you might call it “cleaning the data”. You have to get rid of artifacts from the instrument(s) and perform calibrations so that you can interpret your data properly. The amount of time this takes is highly variable. It depends on several factors including what kind of data you have (imaging, spectroscopy, IFU), and also on how familiar you are with the instrument. It can help to have a pre-made pipeline for data reduction - or it can frustrate the bananas out of you trying to figure out how to run it.
After the data are cleaned you are ready for analysis! This can include an intermediate step, which is referred to by data scientists as “data wrangling”. You want to compare your measurements to some previous study, or mix data from two different sources. Often times these data are in various formats or calibrated to different standards. In order to make everything uniform, you have to perform transformations and/or recalibrate the data.
The analysis will obviously vary depending on the research program, but it might include spectral or image modeling, statistical analysis of data, error and uncertainty estimations, lots and lots of plots, etc. And after many long hours of work you get some results! In some cases this might reduce down to a single point on a single plot, or the results might span many pages of plots.
After all that work, you are ready to begin writing your paper. Some ambitious sorts may have already begun writing as they perform the analysis, but we’ll get to all of that next time on . . . Arbitrary Notations!
Kyle D Hiner
Publishing a paper is a lot of work. I suppose it is easier for some people or for some disciplines, but I have found it usually to take a significant amount of time and effort. Here is an outline of research from the proposal to the finished paper.
First you have to get an idea for your research project. Then you have to write proposals for either or both funding and data. This process itself can be quite intimidating, but it is often exciting. Writing a proposal is a good time to read papers/research from others and get ideas about what to investigate on your own. I often learn a lot at this stage. After you submit the proposal, it will usually take a few months before the results from the review committee are released. At that point, all you can do is wait - or, more realistically, busy yourself with all the other things you have to do.
Once time/funding/data have been granted you can start your actual research program. Going observing is one of my favorite experiences in astronomy, and maybe I can write up a how-to on observing runs in the future. But let’s say you go observing and collect a bunch of data. Then you get to go home and start analyzing, right? Wrong!
First you have to prepare your data. In astronomy we call this “reducing the raw data”. In other fields you might call it “cleaning the data”. You have to get rid of artifacts from the instrument(s) and perform calibrations so that you can interpret your data properly. The amount of time this takes is highly variable. It depends on several factors including what kind of data you have (imaging, spectroscopy, IFU), and also on how familiar you are with the instrument. It can help to have a pre-made pipeline for data reduction - or it can frustrate the bananas out of you trying to figure out how to run it.
After the data are cleaned you are ready for analysis! This can include an intermediate step, which is referred to by data scientists as “data wrangling”. You want to compare your measurements to some previous study, or mix data from two different sources. Often times these data are in various formats or calibrated to different standards. In order to make everything uniform, you have to perform transformations and/or recalibrate the data.
The analysis will obviously vary depending on the research program, but it might include spectral or image modeling, statistical analysis of data, error and uncertainty estimations, lots and lots of plots, etc. And after many long hours of work you get some results! In some cases this might reduce down to a single point on a single plot, or the results might span many pages of plots.
After all that work, you are ready to begin writing your paper. Some ambitious sorts may have already begun writing as they perform the analysis, but we’ll get to all of that next time on . . . Arbitrary Notations!
Kyle D Hiner
Tuesday, October 28, 2014
A Tour of an Active Galactic Nucleus
In my last post I showed an image of an active galactic nucleus. AGN are some of the strangest objects in the universe. Let’s take a tour and see what we find.
Here on Earth, far, far away from even the nearest AGN, what we often see in the sky are single points of light - objects that look much like stars. But these objects have very strange spectra. Spreading the light out over all its colors and wavelengths (spectroscopy), we see that these objects are not like stars at all. They have spectra that are very different from stars. Many show radio emission - not like stars at all. This led to these objects being names quasars - a mashup of ‘quasi stellar radio sources’.
Let’s see what happens if we get closer to the quasar. Astronomers have a couple ways of looking at objects in more detail. We can ‘zoom-in’ by getting better angular resolution; and we can ‘go deeper’ to see faint features in the object. If we do this, we often see that the quasars are just one part of an entire galaxy. It’s amazing - what we saw before - just one point of light - is brighter than the entire galaxy where it resides! And because astronomers like to classify and re-classify objects, we get to rename them. No longer are they ‘quasi-stellar’ - they appear in the center of entire galaxies. It’s a nucleus of a galaxy and it’s doing something, so a better name would be Active Galactic Nucleus (or Nuclei if plural). I know, we’re so creative :P
If we look a little more closely at the host galaxies, we can find entire swaths of gas that are ionized in a strange way. The atoms in the gas get ionized (loose electrons) when energetic photons (light particles) smash into them, and that happens around bright stars. But this gas is ionized in a way that stars can’t make happen. So what is ionizing this gas in the galaxies? It all seems to come from the active nucleus, so let’s get closer to that.
It is practically impossible to resolve the nucleus of AGN, but we can learn a lot about it using other methods. If we could zoom in, we would see some really funky stuff.
We’d see a large toroidal structure of dark, dusty clouds. Because the dust is shaped in a torus, like a doughnut or a fat bike tire, it blocks our vision of the very center of the AGN along some lines of sight, but not others. We think the torus isn’t exactly smooth - it’s more likely made up of lots of individual clouds that travel around the nucleus itself. There just may be fewer of these clouds around the polar regions of the AGN, allowing more light to pass through more lines of sight.
Within the torus we find the “broad line region”, where clouds are orbiting something very massive and very small at the center. These clouds can travel with velocities up to ten thousand kilometers per second. By comparison, the International Space Station travels at about 7.7 kilometers per second (thanks google), and the ISS flies all the way around the Earth in just 90 minutes. So these “broad line clouds” are traveling about 1000 times faster than the ISS.
Getting closer still to the center we find a very bright, very hot disk of material. This is the source of all the light energy that is shinning from the AGN. It is so hot that it glows in the ultraviolet wavelength range of the light spectrum. Just think - your cooking pan gets hot, but doesn’t glow. You’ve probably seen videos of hot metal on the internet that is heated to the point that it glows a bright orange color. And surely you’ve seen fires with blue flames. Well this gas is so hot that it glows in the ultraviolet.
But why is all this gas so hot and traveling with such high velocities anyway? Answer: Within the very center of the hot gas disk, there is a black hole. Not just any black hole - a supermassive one. As I mentioned in my last post, supermassive black holes can be up to a billion times more massive than our sun. And that black hole is pulling very hard on all the gas and dust in the disk surrounding it. The material of the disk is actually falling down onto the black hole itself, making it even more massive.
And if you zoom back out and think about all that gas and dust in the host galaxy that is experiencing the radiation from the active nucleus, you might think that supermassive black hole can have a big effect on the host galaxy. You might wonder if it affects the galaxy’s ability to form stars, or if it affects the shape of the galaxy in some way. And then you might have to get a PhD in astronomy to figure it all out . . . :D
That’s the tour of the AGN, see you next time!
Here on Earth, far, far away from even the nearest AGN, what we often see in the sky are single points of light - objects that look much like stars. But these objects have very strange spectra. Spreading the light out over all its colors and wavelengths (spectroscopy), we see that these objects are not like stars at all. They have spectra that are very different from stars. Many show radio emission - not like stars at all. This led to these objects being names quasars - a mashup of ‘quasi stellar radio sources’.
Let’s see what happens if we get closer to the quasar. Astronomers have a couple ways of looking at objects in more detail. We can ‘zoom-in’ by getting better angular resolution; and we can ‘go deeper’ to see faint features in the object. If we do this, we often see that the quasars are just one part of an entire galaxy. It’s amazing - what we saw before - just one point of light - is brighter than the entire galaxy where it resides! And because astronomers like to classify and re-classify objects, we get to rename them. No longer are they ‘quasi-stellar’ - they appear in the center of entire galaxies. It’s a nucleus of a galaxy and it’s doing something, so a better name would be Active Galactic Nucleus (or Nuclei if plural). I know, we’re so creative :P
If we look a little more closely at the host galaxies, we can find entire swaths of gas that are ionized in a strange way. The atoms in the gas get ionized (loose electrons) when energetic photons (light particles) smash into them, and that happens around bright stars. But this gas is ionized in a way that stars can’t make happen. So what is ionizing this gas in the galaxies? It all seems to come from the active nucleus, so let’s get closer to that.
It is practically impossible to resolve the nucleus of AGN, but we can learn a lot about it using other methods. If we could zoom in, we would see some really funky stuff.
We’d see a large toroidal structure of dark, dusty clouds. Because the dust is shaped in a torus, like a doughnut or a fat bike tire, it blocks our vision of the very center of the AGN along some lines of sight, but not others. We think the torus isn’t exactly smooth - it’s more likely made up of lots of individual clouds that travel around the nucleus itself. There just may be fewer of these clouds around the polar regions of the AGN, allowing more light to pass through more lines of sight.
Within the torus we find the “broad line region”, where clouds are orbiting something very massive and very small at the center. These clouds can travel with velocities up to ten thousand kilometers per second. By comparison, the International Space Station travels at about 7.7 kilometers per second (thanks google), and the ISS flies all the way around the Earth in just 90 minutes. So these “broad line clouds” are traveling about 1000 times faster than the ISS.
Getting closer still to the center we find a very bright, very hot disk of material. This is the source of all the light energy that is shinning from the AGN. It is so hot that it glows in the ultraviolet wavelength range of the light spectrum. Just think - your cooking pan gets hot, but doesn’t glow. You’ve probably seen videos of hot metal on the internet that is heated to the point that it glows a bright orange color. And surely you’ve seen fires with blue flames. Well this gas is so hot that it glows in the ultraviolet.
But why is all this gas so hot and traveling with such high velocities anyway? Answer: Within the very center of the hot gas disk, there is a black hole. Not just any black hole - a supermassive one. As I mentioned in my last post, supermassive black holes can be up to a billion times more massive than our sun. And that black hole is pulling very hard on all the gas and dust in the disk surrounding it. The material of the disk is actually falling down onto the black hole itself, making it even more massive.
And if you zoom back out and think about all that gas and dust in the host galaxy that is experiencing the radiation from the active nucleus, you might think that supermassive black hole can have a big effect on the host galaxy. You might wonder if it affects the galaxy’s ability to form stars, or if it affects the shape of the galaxy in some way. And then you might have to get a PhD in astronomy to figure it all out . . . :D
That’s the tour of the AGN, see you next time!
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